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Equipment Discussions >> Binoviewers

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Eddgie
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Final apeture reduction measurment for EdgeHD 8"
      #6131769 - 10/11/13 07:03 PM

If you have been following my previous posts, you know that I have discovered that the EdgeHD 8" suffers severe aperture reduction if you use to long a light path.

The first time I used binoviewers on the EdgeHD 8", I was appalled at how dim the view was.

I quickly realized that the EdgeHD 8" has a more restrictive back focus than the standard C8.

this was with a 2" diagonal based system, and the aperture was reduced to about 6.2 inches or so.

The first change I made was to go to the Maxbright/T2 Prism, and I noticed a tremendous improvement but with the Baader Clicklock visual back, I was still working at less than 7.6 inches.

I then went to the Mark V and was under 7.5 inches.

This might not seem like much of a big deal, but it constitutes a considerable brightness falloff. Do the math and see for yourself.

Anyway, I then went to a Televue Short visual back, and this got me back over 7.5". to about 7.6" actually.

Next to the Baader SCT to T2 15mm Visual back, and I picked up a little over .1 inch so 7.75 or so.

Last configuration. It doesn't get shorter than this except by going to the Maxbrights, but I wanted the wider true field of the Mark V.

I an now using the Baader 10mm SCT to T2 thread, the T2 Prism, and the Mark v.

I just got around to measuring it today, and here is the final number.

7.85".


I even moved to a NexStar 8SE mount so that I did not have to worry about rotating the diagonal because the 10mm adapter really has only one position and can't be easily rotated.

This is as good as it gets then on the EdgeHD 8" in a large prism.

My estimation is that the 10mm/T2 Prism/Maxbright will be the only binoviewer that will work at full aperture (maybe a millimeter or two short).

Otherwise, 7.85" is about as good as it gets with a Mark V, and no other binoviewer out there will beat the Mark V except the Maxbright, so if working at or near full aperture is important and you don't have the money for a Mark V, I recommend the Maxbright/T2 for the EdgeHD 8".

C5 is going to be about the same. Have not measured it with the 10mm back yet, but I have another T2 Prism on order for that one and will check it when I have it.

I figured it is easier to use the Quick Connect to move the Mark V back and forth than moving the diagonals, so I am putting Quick connect rings on my two SCTs and my refractor so I can easily move the BVs back and forth.

Hope someone has found this info useful.


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Hothersale
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6131783 - 10/11/13 07:10 PM

Do you think you would get 100% aperture with the Maxbright bino, Ed?

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BWAZ
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Hothersale]
      #6131811 - 10/11/13 07:25 PM

Ed, do you use glasspath in all your configurations? I believe the 1.2x GP may save you at least 25mm back-focus, which would definitely alleviate the aperture loss, of coz at the cost of slight true FOV

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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Hothersale]
      #6131874 - 10/11/13 08:10 PM

The Maxbright with the 10mm connector and T2 Prism should come in right at or very very slightly below full aperture in the EdgeHD 8", but it is the only configuration that will do this.

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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: BWAZ]
      #6131900 - 10/11/13 08:21 PM

7.85 is enough that it would be impossible to tell the difference on planets, buf I were wanting to do serious planetary, I would put in the 1.25" GPC and I am confident that this would get me full aperture with the Mark V.

I really have only been talking about the aperture reduction, but the focal length is much shorter now than when I started too.

My initial shock the first time I BVed the EdgeHd was I am sure very strongly compounded by the huge increase in focal length.

In the current configuration, I would estimate the focal length to be about 150mm more than the spec for the EdgeHD 8" says.

Spec says that the focal length for 133mm of back focus is 2125mm. Every 10mm of additional back focus will ad about 31mm of focal length, so I estimate that current focal length with the 10mm/T2/Mark V is about 171mm, or 38mm more than spec, which works out to an additional 120mm of focal length so the total for the EdgeHD 8" in this configuration is about 2250mm.

From all of this, I have become far more anal about back focus in SCTs. It is a real negative and people with SCTs should make every effort to trim every millimeter possible off of their light path even in Mono-vision.

If I ever planned to use the EdgeHD 8" with 2" eyepeices, I would get the baader Cliclock that allows you go screw the mirror box directly to the rear port. I am convinced that this is the best possible diagonal for the EdgeHD 8" and all of the SCTs with 38mm rear threads.

But I don't intend to use the EdgeHD 8" with anything but binoviewers, so not and issue for me.

And this solidifies my position that no other diagonal should be used for binoviewing with the EdgeHD 8". There is no other configuration made that will work at full aperture, and every 10mm or so costs 2.5mm of aperture.

Again, people will think I am being crazy, but do the math for light collection and you get to 20% light loss pretty quickly..


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REC
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6132661 - 10/12/13 09:36 AM

Wow, that is scary...6.2" on the HD! I have been following your posts on all these discussions regarding back focus and aperture loss in SCT scopes. There has been a few solutions posted and if I had 20/20 hindsight I would have bought the Maxbrights for my three types of scopes I'm using. Seems their OCS adapters are better overall than other fixes.

Right now I'm using my WO BV in my refreactors and the Denk2 PS in my 10" Dob and my Meade LS8 scope.

So Ed, do you think I'm getting a similar amount of aperture reduction in my SCT to? The scope is not the traditional design, but the ACF method? I think they use a different secondary mirror to reduce the coma in SCT scopes. Would that be similar to the C HD version scopes?

I'm using a Meade OTA that is 32mm long, then the Meade 2" dialectric diagonal and then insert the Denk PS BV. If I am getting well below 7" of aperture, I definitely want to fix that to get it back into the mid sevens inches.

Bob


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: REC]
      #6133009 - 10/12/13 12:37 PM

I cannot say. I have ray traces or have measured many Celstron f/10 scopes and the C14, and all have lost apeture with back focus starting at between 160mm (EdgeHD 8" and C5) and up to 200mm (C14).

Your scope though is f/8. My bet is that whenever you cross the threshold of apeture reduction, you are loosing more apterture per millimeter of back focus increase than an f/10 scope because of the steeper light cone.

For examlple, if th scope is using a focal reducer, the aperture loss is far more agressive for each 10mm of back focus than at f/10 and there is not a standard SCT that I am aware of that will work withoug loosing aperture wtih a focal reducer past about 100mm of back focus.

But the only way to know (and this is not the first time I have suggested this to you) is to measure it.

Also, jsut look through the darn thing in mono and compare it to bino. If the view does not seem so much dimmer as to make you feel like you are loosing to much brightness, then ignore it.

Different people will of course have different threasholds. I can see a 20% transmission loss with no difficulty and don't want to accept it.

Some people might be happy with a 40% transmission loss.

Only you can say what is acceptable.

If it it doesn't bother your enjoyment of the scope, ignore me because what I am saying is not important.

If you fell like it could be better though, then measure the apeture and calculate how much you can gain by going to a shoreter light path. You may find that you are not willing to make enough compromise to make it worth it.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6134449 - 10/13/13 08:01 AM

Edd...

Measured aperture at 178mm with

8" Edge
Baader 2" cliklok visual back
Denk 2" WO diagonal with filter switch and power switch attached
MK V binos attached to the above with Baader T2 quickchange adapter
Power switch in reduction mode (.7x reduction approx)

Will try soon with straight thru mode on the power switch.

So am operating at approx 7" aperture in this configuration.

Seriously thinking of going the BAADER prism route and losing the 2" diagonal with power switch setup....
But...do love the convenience of the power switch

What to do....i guess i will test with my eyes on some doubles, the moon and jupiter to see if the loss of 1" aperture really makes a difference to me.

Any comments?


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REC
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6134621 - 10/13/13 09:57 AM

Howard, that's just about what my configuration is with my 8" SCT, so it looks like I'm about 7" as well.

Ed, BTW the scope is an f/10 not f/8 in this ACF design. I think you once told me that with my 2" backend configuration I was working at something around f/13 now.

Bob


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6134735 - 10/13/13 10:51 AM

Is your setup the WO diagonl with a dovetail that allows you to attach the Powerswitch directly to the top of the diagonal?

Every 10mm of back focus you can cut out will buy you about .1" of apeture.

Now restoring .5" of apeture sounds like a little thing, but you have to consider that the outside of the light cone is where a disproportinate amount of the energy is because the outside 10mm of mirror has more are than the next 10mm of mirror and so on.

Here is the math for an EdgeHD 8".

The collection area with full apeture is about 50 sqaure inches, but you loose about 5 square inches to the seconary mirror shading so you have a total of about 45 squre inches of light collection.

If you cut one inch of the mirror off, you reduce the lighht collection area of the primary to about 38.5", but you still have to take the same 5 square inces off for the secondary shading so this puts you at 33.48 square inches.

That is a 33% light loss.

It gets worse though becaues that 34% obstruction when the scope is working at 8" becomes a 38.75 obstruction.

And bad news.. I bet you did not make the measurement with the low power arm in. When you put the low power arm in, you have to move the mirror even further forward, and this takes another .4" of aperture, so with the low power arm, you were likely working a about 168mm.

This would give you 34.4 square inches of light collection for the primary minus the 5 sqaure inches for the secondary, for grand total of 29.5 square inches. Now you are bascially into 6" refractor area.

None of these figures take in to account the normal 10" transmission loss of JUST the SCT, much less the diagonal, splitter, and prisms in the binoviewer, but since these are common to all configurations, we can ignore it. Anyway, with 29.5 square inches of light collection, you are not working at 52% of the brightness of a full apeture scope.

Compare this to a Mark V working at 7.85" and using a pair of 35mm Ultimas. Hmmmm.

Your diagonal is likelly a light path of about 3" or 75mm or so from the front of the mirror box to the mirror face and on to the top of the mirror box.

going to a T2 Prism would cut about 37mm and going from the Clicklock to the 15mm SCT to T2 would buy you another 20mm or so.

This would give you 57mm of light path savings, and this would buy you back about .5" to .6" of aperure and lower the focal lenght of the scope by about 180mm.

Let's be optimistic and say that it is .6 apeture improvement.

Now the scope is working at 7.6" in straight though mode and about 7.2" in reducer mode.

In straight though, you would be getting about 45.3 square inches of light collection at the prmiary minus the 5 swuare inches of the secondary, so 41.36" total.

This is only an 11.3% loss when going straight though.

Loss when using the low power arm will be about a 26% loss, so a huge improvement over the 50% loss in the current configuration.

I have been ranting on this for a year now.

Most people simply look at a little apeture ruduction as no big deal, but they dismiss the amount of energy that is contributed to the image by the outside of the light cone.

My own configuration the first time I binoviewed an EdgeHD 8" was a 2" visual back with 40mm of light path, a 2" diagonal with eyepeice holder (about 100mm of light path), a power switch (18mm of light path) and a binoviewer with 128mm of light path.

Even in straight though, the scope was working at less than 7" of aperture (about 6.6" by my calculations and 6.2 with a low power arm but at the time I did not know how to measure this). I knew immediatly by looking though that something was seriously wrong.

When I changed to the Maxbright T/2 the improvment was (to me) dramatic.

I would rather work at 7.85"" with a pair of 35mm Ultimas for low power work than use any kind of reducer will will at the very best case reduce the aperture between .4 and .6 inches. Even the Glee telecompressor costs .5" and it is designed to work with binoviewers.

Only you can decide the compromises you are willing to accept.

But that is the way you do the math on it. Expect about .1" loss or gain for every 10mm of light path you add or take away.

Loosing the Diagonal by itself may not buy you much, but combined with loosing the Baader Clicklock, it could make a big differnece.

And that has been my message. A little change doesn't make a difference that is easy enough to see and may not be worth it.

Once you do the math though, it can become apparent that making a big change will pay off.

There is no diagonal I would use an an SCT with binoviewers other than the standard T2 prism, and as inconvenient as it might be, the only way I would connect it would be with the 10mm SCT to T2 connector. If the scope is GEM mounted, I would still use the 10mm connector and I would add a Baader SCT lock ring. This adds about 5mm, but it is far easier to use than the standard 15mm connector's SCT type collar, which is not a good idea for a binoviewr. The SCT lock ring with 10mm connector is the right way to go.

If you did not make the measurement with the low power arm in, I would be intrested to see what you get. I have been conservative by saying .4" of aperture, but it is as I recall actuallly a bit closer to .5".

And this is simply math. You can calculate the image brightness change pretty easily once you have the back focus difference.

I know that people will probably think I am ranting about it, but I am only trying to make people aware of the reality here. It is impossible to get any SCT to work at full apeture when using a binoviewer and any kind of reducer, even with the T2 prism.

By keepng the lgiht path as short as possible though, you can greatly minimize the impact of the apeture reduction.

I hope this helps, and I encourage you to measure with the low power arm in and give us the figures...


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6134932 - 10/13/13 12:41 PM

This was with the low power arm in
In reduction mode
178mm


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135048 - 10/13/13 01:43 PM

That is excellent then.. It proves that your efforts to keep the light path short have been effective.

But this is with the Mark V and that is a shorter light path than the Denk, so that accounts for some of the difference.

Did you measure the apeture straight though with no power arms?

The first coniguration I used where I had such bad result was a Clicklock, Televue 2", and Denk Powerswitch.

Aperture reduction was pretty horrid.

In your case though, you may be working at full apeture with the high power arm in, and that is where it is most important because that is when you are observin planets.

And some of the lower power apeture loss is offset by the bigger exit pupil.

But working with a reducer at 7" is pretty good.

I was able to get the C14 working at 13.5" with the Binotron by goiing to the T2.

With a standard 2", apeture was something like 12.6"

So now you know that for about every 10mm you cut, you can improve the apeture by about .1 inch.

If you cut 57mm, you can get to about 7.5" or 7.6" and that is still a meaningul increase in brighness.

One of my key points has been that you really don't know what you are working at until you measure it.

And your improvement over what someone using a standard 2" diagonal with eyepeice holder and a longer light path binoviwer unit is probably about .3 to .4 inches because your bino light path is shorter and you have eliminted the eyepeice holder from the light path.

But 7" is excellent for reducer mode. As I said earlier, best I have heard of with a reducer was with a Glee in front of a Maxbright in a C8, where I think the measured apeture was only .5" doan.

Would love to know your apeture though straight through. and your total light path. Have you measured it? Mark V is 123mm.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6135177 - 10/13/13 02:49 PM

Not measured aperture straight thru.

Will post a photo soon for your comments


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135214 - 10/13/13 03:08 PM Attachment (9 downloads)

photo...

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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135218 - 10/13/13 03:09 PM Attachment (7 downloads)

and....

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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135232 - 10/13/13 03:20 PM

Do not know how to measure my total light path..

Pls tell me, Edd


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135259 - 10/13/13 03:33 PM

If you want to do it, you would start by using a ruler or caliper to measure from the flat at the rear of the SCT port (inside the Clicklock back)to the end of the visual back.

This will usually be about 30mm or 40mm. Not the outside, but the inside from the rear of the port to the end.

It is hard to measure the diagonal.

Best you can do is approximate.

Measure along the side from the front of the mirror box to where you think the center of the mirror would be.

Then again, from the center of the side of where you think the front of the mirror would be to the top of the mirror box.

For most 2" diagonals this is about 1.5" front to center, and about 1.5" center to top.

Now, just measure to the top of the mirror box to the top of the Powerswitch to get the total light path to the top of the part where the T2 thread is.

Now, add 123mm for the light path of the Mark V.

Total it all up.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6135270 - 10/13/13 03:41 PM

How does it all look to you Edd?

Long light path or what?


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6135275 - 10/13/13 03:43 PM

I have to say that I am surprised that you would be getting as much aperture as you report.

I estimate that you are at 250mm of light path.

Are you sure that you were at infinity focus when you made this measurement?

Based on a 250mm light path, your aperture should be 7" when straight though.

If you focused without the powerswitch, then slid it in to make the aperture measurement, then you are getting the spacing for straight through.

Any time you measure, you have to ensure that you are at infinity focus for that specific configuration.

If your result with over 230mm of back focus was this good, then there must be some difference between our telescopes. My EdgeHD 8" starts to loose aperture right at 160mm of back focus.

I have measured it in a half dozen configurations and it always works out about the same, with each 10mm past 160mm taking about .1" of aperture without the reducer, and about .13" with the reducer.

So, not sure where the discrepancy is coming from, but with 171mm of back focus on my scope, I am at 7.85".

But that is why I keep telling people to measure for themselves.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6135295 - 10/13/13 03:55 PM

Edd...

I am fairly sure i was focused at infinity with the left reducer arm in.

Least the arm was in from the last session .....usually when i bring the scope in doors i leave the focus and powerswitch where it was when i turned the off switch.

Will check though


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A6Q6
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6135305 - 10/13/13 04:00 PM

Eddgie, tell us you didn't get rid of your C14!

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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6135447 - 10/13/13 05:28 PM

That is a pretty big difference between my scope and your scope.

I was under 6.5" with a baader Clicklock and standard 2" diagonal, but no filter switch, and also using a scope with a longer light path than the Mark V.

Again, perhaps there is some difference in our scopes that is making mine work differently.

If you could make the light path measurements and double check that you did the measurement at low power at infinity focus, I would really appreciate it.

Perhaps there is something in my scope that could be changed to improve it.

Again, this is why I encourage people to measure though. You don't really know what you are getting until you measure.

7" is not bad for having a reducer. Still a 34% light loss though, and if you can shorten up by 50mm, that will put you at 7.5", which is only a 15% light loss, that still gives a 20% improvement.

20% is only very moderate improvement though, so if you are happy with it, it may not be worth dumbing the 2" diagonal. Only you could say.

You might though want to do the math to see how using the Mark V with 24mm Panoptics or 35mm Ultimas might work out.

You may find that the power is not all that different and that you can get almost as wide a field at a bigger exit pupil when you factor in the light loss.

But this is academic really. If you are happy with the way it is, there really isn't any need to do anything and you can simply enjoy it the way it is.

I am curious about the disparity though. I would have calculated well under 7" of aperture based on my own configurations.. If your measurements confirm your original readings, then there must be an issue with my scope.


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: A6Q6]
      #6135464 - 10/13/13 05:38 PM Attachment (14 downloads)

C14 has passed to a new owner.

I love it and enjoyed it for many years, but had been waiting to buy a Go-To dob.

The CGE 1400 was simply getting to much to move in and out, and it took too much room to leave on my covered patio.

The new scope has a very small footprint and can be left on the patio in a sheltered corner and deployed in a couple of minutes with a hand truck. So, 12" stays outside 24/7. CGE on a cart would have been to big.

The other factor was that I simply could not get much true field using binoviewers and the 12" dob is far better in that respect.

The primary driver though was the desire to simplify the setup routine and the 12" has been simply fantastic from that standpoint.

So, was time.

The 12" is of course giving up a little light, but I get a much wider field of view, so I am happy with the trade.

Been revisiting a lot of targets. Globulars are not as good, but most other targets are still very satisfying.

Have not really had much chance to do planets or the moon but seems like it will be good enough.

Edited by Eddgie (10/13/13 05:40 PM)


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REC
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6136738 - 10/14/13 11:41 AM

Nice pic of your new scope! Where do you observe from, backyard area and if so, what is your LP level there, red, yellow zone type of sky?

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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: REC]
      #6136915 - 10/14/13 12:56 PM

I am in Austin Tx about 4 miles north of downtown, but central neighborhood.

Lot of tree canopy, but still most nights VLM is 3 or 4 if I am lucky.

But I do an enormous amount of observing in terms of catalog objects. Brighter galaxies only, but tons of planetary nebula, Globulars, and clusters and doubles and most of these are still really excellent.

Of course better under dark skies, but the nearest dark sky observing site (where the skys are really black and you won't get shot at for being on the edge of someones private property... Yeah, this is Texas and they $**T like that here) is 70 miles away.

But the scope has been working great. It is a heavy sucker, but I can move it on a hand truck and the alignment is really fast because you don't need to do any kind of home position. I really like that.

And if you only want tracking, you really don't even need to use a star!

Sweet.

Once I got past the weight, I was really happy with the telescope and Go-To, and it is great with the Binoviewer and 1.7x coma corrector. I can't use to low a power anyway because the sky washes out, so is working fine.


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A6Q6
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6137123 - 10/14/13 02:07 PM

Well, I'm very sad to see you part from your C14, for me its like when Erik Bakker over on the Questar forum, sold his Questar 7 and now uses a 16" dob. I always liked the fact that you could speak from a position of authority when people talked about the C14 vs 6" APO . I hope when you start L&P observing that those Orion optics hold up. But you can always send them out to have them reworked.

Edited by A6Q6 (10/14/13 02:09 PM)


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: A6Q6]
      #6137525 - 10/14/13 05:28 PM

I had budgeted to have the Orion mirrors refigured if they were at the lower end of the quality spectrum, but they were better than that, and if fact, I would say pretty decent. The secondary breakout is fairly well balanced, and there are no zones, no sight of turned edge.

I am sure everyone would be curious about why I sold the C14 and kept the 6" APO.

I was going to sell the AP, but my assistant astronomer really balked. She remembered how much I wanted it and thinks it would be a mistake to sell it.

Have not used it in a year though. If it fits in the field, I prefer the EdgeHD 8" because it goes a tiny bit deeper and has the same excellent off axis performance and it is a lot easier to get out of the door.

I have considered putting the 6" APO on a DM6 or something to make it easier to use, but I am not so much into low power scanning.

So, will keep it for the time being, but I suspect its days might be numbered.

I am really enjoying the ease of getting the 12" dob on to the firing line, and once I get a coma corrector for the 31mm Nagler, I simply can't see myself using the 6" APO again. The 6" dob with the 31mm Nagler will have only a little narrower field of view, and a lot more horsepower.

But I still might keep the refractor. It will be the only AP scope I will ever own, and it really is a lovely telescope to use if you can be happy with 6".

I am lucky to own one telescope that is pretty much perfect at everything it does. 6" Though. 8" would have been better.. LOL.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6137566 - 10/14/13 05:52 PM

You sure make the most out of this hobby even in a limited sky....what dedication! Yeah, I really enjoy your enthusiasm in your posts and have learned a lot especially in the world of binoviweing, you help a lot of people out and seem to be able to enjoy it as well:)

Clear skies to you


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: REC]
      #6137583 - 10/14/13 06:03 PM

Yup

I also get a lot out of Eddgie's posts on all forums he is at large on.

Very knowledgeable and prolific


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6137873 - 10/14/13 09:18 PM

Too much. I need to cut back.

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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6138499 - 10/15/13 08:19 AM

Put a Herschel wedge with binoviewers on that 6" AP, Ed.

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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: A6Q6]
      #6138653 - 10/15/13 09:46 AM

Quote:

Well, I'm very sad to see you part from your C14, for me its like when Erik Bakker over on the Questar forum, sold his Questar 7 and now uses a 16" dob.




I am sorry about that

Love my MW 16" f/5 though, it is a big step up from the wonderful Q7 in planetary observing and has it's own superb user friendliness


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Erik Bakker]
      #6138898 - 10/15/13 12:06 PM

Hi Erik, I know you and Eddgie wouldn't settle for anything less, and I know you have to move on. But the Q7 & C14 are scopes that many people who have been in the hobby a long time have admired, and for whatever reason, couldn't have. I will still always enjoy what you guys post.

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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: A6Q6]
      #6138985 - 10/15/13 12:47 PM

Well, just because we have changed scopes doesn't change our experience with them.

And new scopes mean new insights.

For example, the 12" is not as comfortable to use as the C14, and the off axis performace even with a coma corrector is not as good as the 6" APO.

I have had Newts before too. My first large telescope was a Meade 10" f/4.5 Newt (GEM Mounted).

So, Newt is not new territory for me at all.

Changes sometimes result from change in requirements, thats all.

No reflection on the C14. I have seen more with it than all of my other scopes put togehter I suppose.

Seriously, I have viewed maybe 1000 different objects with the C14. Most so faint that I could barely see them.

But the 12" offers new possibilities, and will do things the C14 could not do.

Just a different instrument with different capabilities.

I always said that if I had an observatory, I would have the C14 in it, but I guess that is never going to happen.

And the convenience of the Go-To dob became compelling in my own case. I had waited for a well integrated Go-To dob, and I knew that when one came along I would buy it.

And it did, and I did what I had wanted to do.

Don't worry, be happy.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141244 - 10/16/13 04:36 PM

Eddgie....

Edge8" with baader 2" cliklok visual back, mk v binos on 2" diagonal with powerswitch and filter switch with the baader quick change lock on top as shown on my fotos gives...

178mm aperture in reduction mode
185mm aperture straigh thru mode

So straight thru i am at 7.3 inches aperture....not so great.

If i remove the whole 2" diagonal/power/filter switch thing and insert a baader zeiss prism diagonal into the cliklok visual back with its quick change lock on top and then clip on the mk v's .......i do get 200 mm aperture....or....the full 8"

Compromise then for me...

Live with a 7-7.3" aperture but being able to flick thru 3 magnifications without changing eyepieces or go the full 8" but only one magnification.

I do not really look at DSO's...from my backyard....more planet, moon and difficult double stars

What say you?


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6141330 - 10/16/13 05:19 PM

Well, getting 178mm is a lot better than I got with a 2" diagonal and a powerswitch binoviewer but I was also using a binoviewer with a 127mm light path. It all adds up.

So, the WO diagonal has indeed paid off for you for low power.

But as you can see, straight though, there was a penalty.

Still, you are doing better than I am because even with the 10mm SCT to T2 adapter, I am getting 200mm where you are getting 200mm with the Baader Clicklock.

I can only think that there may be some slight difference in our scopes to account for the .1" difference in aperture reduction that appears to be occurring.

Even with the Televue short adapter (30mm of light path) I was only getting 7.7".

Did you measure your light path? Just curious.

7.3" is a big hit. Only you can judge if it is meaningful enough difference, but for planets, I think you would do better to go to the BV/Prism You are loosing 22% brightness, which combined with the binoviewer dimming, is giving you about the same brightness as you would get with maybe a 6" telescope the same magnification, and the contrast loss is going to be a little more of course because while the aperture is reduced, the size of the secondary is not, so the percentage grows.

I am also again bit surprised by the fact that your aperture was only reduced by .3" with the low power arm.

I got .4" to .5" of loss depending on the configuration, but again, I was using a regular 2" diagonal and a binoviewer with a longer light path (The Mark V really is short considering the giant prisms being used, yes?).

Only you can really say for sure if the compromise matters. Your system is working a bit better than my system did, but as you can see, there is always some kind of compromise.

Again, your scope seems to be getting a bit better result, but I would really appreciate it if you could measure your light path. Perhaps I over-estimated yours. I think the diagonal your are using may be shorter than I would have guessed.

Again, thanks for the measurement.

And yes. All about compromise. But I totally get the desire to have the powerswitch.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6141337 - 10/16/13 05:22 PM

Also, this.

What is the lowest power eyepiece that you use for low power arm? Are you using anything like 24mm Pan or ES???

I tried 24mm Hyperion in a powerswitch system and got pretty noticeable vignetting with the low power arm.

Would be good to know your light path...


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141345 - 10/16/13 05:27 PM

And one last thing.

Remember, when you put in the high power are, if you don't get too much power (which was a problem I had many nights) for planets, remember that you will pick up a couple of tenths of an inch of aperture because you have to move the mirror forward to re-focus.

You may want to measure it. This might mean that you have 7" for low power, 7.3" for medium, and maybe 7.6" for high, and 7.6" would not be so bad really for planets.

Again, one of the problems I had though is that if I went with a 20mm ES (no vignetting in low power) I would get too much magnification for most nights with the high power arm in, so I was forced to change to a 25mm pair anyway, which kind of defeated the purpose of the powerswitch.

But if you don't want to re-configure, putting in the high power arm and going to longer focal length eyepeices might be a good way to brighten the image and lower the power a bit, because you get back some aperture as well.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141435 - 10/16/13 06:05 PM

And one more "one more thing."

The reason that I was hoping to get your total was to see is the .1" loss per 10mm figure is otherwise accurate.

If aperture reduction starts at 160mm (though it may be starting at 170mm on your scope), that would according to my estimate mean that your light path is 240mm (230mm if your scope is starting to loose aperture at 170mm).

By knowing the light path as exactly as possible, we can see if the 160mm figure I came up with is working.

Also, what eyepiece were you using to make your measurments?

I had .1" extra when I used 40mm Plossls because these have ffield stops very low in the barrel.

With the 24mm Hyperions, I go the most aperture reduction because the field stop is pretty far back in the barrel. I started using the 24mms for all measurements because it was the eyepiece I used the most.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141483 - 10/16/13 06:26 PM

Eddgie

I was using a pair of 16mm Naglers for the test.

I cant understand how to measure the diagonal light path or the cliklok visual back light path
Can u post a photo or diagram showing me please


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6141582 - 10/16/13 07:04 PM Attachment (17 downloads)

For the Clicklock, just insert a ruler into the rear of the Clicklock and let it go until it touches the flat at the rear end of the SCT's rear port. Now, measure from the flat at the rear of the SCT port to the end of the Clicklock. This should be about 34mm to 36mm.

For the diagonal you need to make two measurments.

Just lay the ruler along the side of the mirror box and measure from the front to the where you think the front center of the mirror is at. Unless you are willing to touch the mirror itself, this is really the only way to do it.

Then, measure from the center of the mirror to the top of the mirror box.

Finally, measure form the top of the mirror box to the bottom of the Quick Connect ring (the BV light path includes the dovetail I think).

Yellow in pic... Notice that from front to center, about 1.27" front to center, and another 1.27" center to top of mirror box, for a total of about 2.54" or about 64mm just for the mirror box on the diagonal in the picture.

From the top of the mirror box to the top of the eyepiece holder on my diagonal is another 1.5" or another 38mm

You of course do not have this top piece (consistent with my advice to not use a standard 2" diagonal), but my entire light path for the 2" diagonal is about 92mm.

You though may be at the 54mm or maybe even shorter which would be really excellent for a 2" diagonal configuration.

So, for you, you would add the Clicklock, mirror box, and top of the box to the bottom of the quick connect ring, then add 123mm to that..


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141610 - 10/16/13 07:18 PM

My bet is that the Clicklock is going to be 35mm or so, and 54mm or so for the diagonal for a total of 89mm.

The powerswitch I think is 18m and the filter box looked like another 15mm or so, with some kind of attachment, so that would be 10mm.

Add the 123mm for the Mark V, and I get a total of 255mm.

If that is the case, it puts you 95mm over the point where I think my scope starts to loose aperture (160mm) and in my scope, this much back focus would cut me to about 7.1".

So, my guess is that either I have not estimated your total path well and you are shorter than this, or for some reason, my scope is loosing aperture with a bit less back focus than you are.

But I was guessing on your back focus really, and my formula is not exact, just an approximation (2.5mm for loss for every 10mm of back focus).

In fact, now that I am thinking about it, I have been saying 10mm for 2.5mm of aperture loss, but in fact, it may be 11mm and I just used 10mm to make it easy for people to remember.

This would give .85 aperture loss and this is closer to what you are getting, so my mistake for using 10mm as a convenience.

I just thought when people were dealing with 20mm or 30mm light path change, it would just be a little rounding error.

We can do the math when we get your numbers...


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141653 - 10/16/13 07:38 PM

I had this thought too.

Some of the difference in the reducer measurement may be due to the fact that my light path was almost 280mm the first time I measured. I was using a Clicklock, 2" diagonal with eyepiece holder, a powerswitch and a BV with a light path of about 130mm. Total was almost 280mm, so my system was already working at a much longer focal length and maybe my reducer measurement was affected by this.

Perhaps because you are using the reducer with a shorter light path BV, you don't need as much mirror travel.

I bet that is the difference. One would not think that 7mm light path would matter between the reducer and the eyepiece field stop, but it could mean less mirror travel in reducer mode.

So, a wild car. I was using Denks....

The difference could amount to .1" of aperture and that tallies good with my .4" to .5" loss for the reducer in my configuration vs. .3 in your... I had a much longer focal length to start because of the longer light path, and my BV was longer light path than the configuration with the Mk V.

That is why I tell people that they need to measure...



Edited by Eddgie (10/16/13 09:21 PM)


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6141707 - 10/16/13 08:05 PM

On a related issue: WRT minimizing the binoviewer light path and eyepiece field stops, Sterling plossls are one of the worst eyepieces to use needing a lot of in-focus. Ortho's are one of the best, with around 20mm difference in the focus position compared to the Sterlings and Televue plossls and Panoptics are good with about 15mm difference in focus position compared to the Sterlings.

I wonder where the field stop of the Denk eyepieces is compared to others?


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6141850 - 10/16/13 09:31 PM

Yes, the Telvue 40 field stop is right at the bottom of the barrel, so they take the least amount of infocus.

35mm Ultimas are hard to understand. They have a field stop near the bottom like the TVs, but take far more in-travel.

Anyway, it could be a factor if HowardK is using an eyepiece that takes less in-travel.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6142288 - 10/17/13 05:16 AM

Eddgie

Cliklok visual back.....35mm
WO 2" diagonal.......88mm
Power/filterswitch.....63mm
Mkv..........123mm

Total.....309mm
I use 16mm NAGLERS pretty much all the time.

Loooong light path eh?


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6142537 - 10/17/13 09:42 AM

Ok, then there has to be some issue with my particular scope.

When I used 280mm, I was working at less than 7" even straight through.

So, my information is wrong and I will have to stop giving it out.

Perhaps they have changes something in the design so that the scope does not loose apeture until 200mm, which is the way the old C8 was set up.

I was under 6.5" with low power arm so again, much worse result than you are getting though I was also using a different binoviewer and I wonder if the binoviwer itself was somehow contributing to the differnce???

Again though, that is why I tell every one that if they really want to know, they need to measure for themselves.

So, has to be something different in my particular EdgeHD, which was one of the first delievered to the US or something with the Denk II that I used for these measurments.

But in the C14, the result was similar in that I was reduced to 12.5" with reducer in a 2" configuration, and improved to 13.5" with reducer by going to T2 prism and 13.9 straight through (full apeture with the Mark V and with the Binotron used with just the prism and no powerswitch.

I am happy with it now though, but you clearly have a better functioning system than I had.

If someone using a Denk II withs a 2" diagonal and power switch could make the measurement, then we would know for sure if the difference is in the EdgeHDs or perhaps an issue with the Denk II itself.

You are still loosing apeture of course, but much less than my "simple formula" would have calculated.

Has to be an answer, but we may never know...

Once again, people should measure if it matters to them.

You are lucky though. That is not nearly as bad as I would have calculated, so my data appears to be fautly, but don't know if it was becasue of some difference in the scope, or difference in the Binoviewer being used....

Edited by Eddgie (10/17/13 09:52 AM)


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6142661 - 10/17/13 10:47 AM

The more I think about this, the more puzzled I am.

I have done this measurement with three different scopes.

With the C5, my apeture reduction using a 2" power switch system and 30mm visual back was something like this (and I don't have the numbers, just going from memory).

With the 2" diagonal and PS in the C5

99mm In low power, something like 112 in straight though, and something like 119 in high power.

With the 1.25" diagonal, these went to 110mm in low power to something like 119mm with straight though and something like 123mm in high power.

And for the C14, it was much the same.

I think with 2" it was something like 12.6 in low power, 13.4 in straight though and 13.9 in high power.

With 1.25" it was something like 13.5" in low power, 13.9 straight though, and I did not measuer in high because I was sure it would be full apeture.

And of course the EdgeHD 8" was even worse than these.

So I am really struggling to understand why the result is so different.

The C5 was loosing 1.1" (a bit more than you) but I had a 10mm longer light path and the C14 was not that much different from you.

But muy EdgeHD 8" is clearly not working the same, while yours is working even better than any of my scopes did.

Some of it might be some difference in the binoviewrers, but some of it has got to be some issue with my EdgeHD 8".

I still beleive that keeping the light path short is beneficial, but I have to back off on providing any kind of general guideline now, and instead just suggest to people that if it matters to them, they need to measure for themselves.

I wish I knew why the discrepencey was so large though.

And when I thought about it, when you were configured about the same as I was using the same binoviewer, you were still working at less than full apeture, but still with a much longer light path, so that would rule out the binoviewer.

My light path with the 10mm/T2/Mark V is 171mm, and I am only getting 200mm. You have 60mm more than I do and you are still working at the same apeture.

Has to be something with my EdgeHD 8". There really isn;t any other explination, and this would mean that what I have been telling people is very innacurate.

I have though been careful to tell people that they should measure for themselves, so at least I can say that I was open to accepting an error in my data.

Edited by Eddgie (10/17/13 10:54 AM)


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6142855 - 10/17/13 12:29 PM

Eddgie

I am going to recheck my aperture measurements again in reduction mode and straight thru

Just to be certain


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6143611 - 10/17/13 07:53 PM

No, you have checked them twice already. If you got the same thing both times, I think that is pretty reliable.

I think it must be something with my scope.

Your result is far more consistent with the standard SCT and I was really quite surprised to see the reduction starting so early on the EdgeHD 8".

So, my bet is that your outcome would be the same. Has to be some difference in my scope.

Maybe my baffle is sticking out further or something.


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6144239 - 10/18/13 04:09 AM

I did a measurement with my 8" Edge to add to the list.

Baader Cliklock visual back, 1.25" Tak prism diagonal, WO binoviewer and 25mm Televue plossls gave an aperture of 192mm (between 7.5" and 7.6")


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6144466 - 10/18/13 09:18 AM

That is interesting because that between our measurments.

If your visual back is 35mm, a standard 1.25" diagonal is about 70mm, and the WO is about 110mm, so you are at about 215mm light path.

If we loose 2.5mm for every 10mm of back focus (and this is aproximate, you are starting to loose aperture at about 175mm.

This seems much closer to where I loose aperture than where HowardK does. Interesting...

With his setup, it would appear that he is not loosing aperture until 230mm of back focus.


Very strange.

My guess is that his baffle tube is shorter than ours. I would guess this because it is the primary baffle that hits the light cone first as the mirror is moved forward.

Our baffles may be about the same length, but perhaps is is 5mm or 6mm shorter.

Very interesting. Wish we could measure baffles of all three to see.


So, for you, if you were to use a 2" diagonal, you would also drop below 7" I think.

It would appear thought that there is some variability, and for this reason, people should measure.

Also, my formula (10mm = -2.5mm loss) may not be accurate.

Interesting....


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6144514 - 10/18/13 09:43 AM

Just eyeballing the baffle, the length of the baffle sticking out past the mirror slide safety ring appears to be similar to or slightly longer than the width of the end of the baffle.

Edited by tonyt (10/18/13 09:44 AM)


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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6145289 - 10/18/13 05:33 PM

Have you measured your light path? I just estimated, but I could be wrong on the diagonal. Most 2" diagonals though are about 70mm light path.

I am not sure if looking at the baffle that is sticking out in front of the mirror is reliable, because the mirror would have to be fully to the rear.

I think that the difference would be where the baffle is threaded into the rear cell. If my baffle is not screwed in as far as yours or Howards, then he could push the mirror further forward.

But the difference here is pretty extreme. Even with over 300mm, Howard is loosing only .7", and if the formula I have is even partly correct, I would have thougth that he would be under 7".

You are much closer to me. When my light path was 191mm, I was at 7.7". Taking off the Televue short back (30mm) and going to the 10mm SCT to T2 got me to 7.85" so just a bit short of .2" for about 20mm of light path.

The only possible explanation is that his baffle is screwed in deeper.


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6145413 - 10/18/13 06:54 PM

Quote:

The only possible explanation is that his baffle is screwed in deeper.




There could have been a manufacturing change or there could be errors in measurement - we have 3 different people doing the measuring (not meaning to be impolite, it's just a possibility). It would be useful if another owner of a recently purchased scope could do a measurement - mine is 2 or 3 years old, purchased second hand (very nice optics though ).

Edited by tonyt (10/18/13 06:59 PM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6145752 - 10/18/13 10:32 PM

Well, there is always the possibility of error in the measurements, but I have done mine many times, and get pretty consistent readings.

Also, I have measured C5 and C14 as well, and my "Formula" (which may not be that accurate) was based on the fact that all three tended to behave the same way once aperture loss started.

And I have measured in 2" and 1.25", and the result was always the same. If there was aperture reduction, for about every 10mm or 11mm of back focus I could cut out, I restored about 2.5mm of aperture (.1").

These measurements are kind of hard to take though, and are not all that exact, but overall, this is about the way it averaged out for me

I think that this latest measurement is closer to mine though.

Would be helpful though is we knew your light path. I am only guessing, and there is nothing like a ruler to make sure.

Also, I am estimating the WO binoviewers to be similar to the Maxbright, but I don't know if that is the case. They are about the same size though, so I expect that 110mm is about right, and I doubt that they are shorter than the Maxbright, but they could be a bit longer.

I think going with 110mm is about right.

Not sure about the Tak diagonal, but most 1.25" diagonals are between 60mm and 70mm.

Assuming that the prism is about the same size of the T2, then the path though the housing is most likely about 40mm, and most of these have an eyepiece holder about 25mm, so I would be surprised if it was much shorter than 65mm, and would bet that it is a bit longer than this.

So, it would be good to have a close measurement.

My EdgeHD 8" is also a few years old. One of the first sold.


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tonyt
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6145882 - 10/19/13 12:14 AM

My light path:
Using measurements others have done for the diagonal and bino rather than taking my own measurements in a refractor, I come up with 207mm from the end of the rear cell threads.

Tak 1.25 diagonal: 64mm
WO Binoviewer: 108mm
Cliklock VB: 35mm (not including the part that screws onto the rear cell threads)

Edited by tonyt (10/19/13 12:22 AM)


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Eddgie
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: tonyt]
      #6146357 - 10/19/13 10:26 AM

Interesting.

See, this is much closer to what I get in terms of aperture loss.

I am at 171, and I am loosing .15", but I calculated about 2.5mm for every 10mm of added length.

Your length is about 35mm more than mine, so this would suggest an additional (3.5 x 2.5mm) an extra 8.75mm of loss over my .15mm, for a total of 8.9mm of loss.

And that would put you right at (203 - 9) 194mm.

Now the difference of 2mm is 1% of the total aperture, and this I think 1% difference is within the margin of error for the test (this is what I think other testers have come up with and I believe that the diffraction caused by the light coming out of the baffle actually does make the test difficult to interpret with 100% accuracy).

It would appear that your scope is working almost exactly the same as mine though, with aperture loss starting at maybe a tiny bit longer back focus than my own, but in general agreement.

This would indicate that aperture reduction is indeed starting on our scopes at about 165mm and that every 10mm or 11mm of additional back focus takes 2.5mm of aperture.

I am at a complete loss to explain HowardsK's superb result, but it can only be a factor of the baffle being shorter. There really is no other explanation.

And it would have to be a lot shorter, because even the standard C8 looses more aperture than he is loosing.

I am perplexed how his instrument could have such a fantastic result though as compared to ours.

If you were to measure with a 2" diagonal, it would be interesting to know what your result was though.

But I would not expect you to do that. I know from first hand experience how tedious it is to do these measurements.

I did about 6 different measurements on the C14 and it was simply to tedious that I stopped after that, but not before I had a pretty good ideal of the situation (aperture reduction at about 200mm, and again, about .1" per 10mm of additional light path)

Thanks for reporting this though. We now have three data sets and they all have one thing in common. All three scopes were loosing aperture in the configurations measured.

I feel better (at your expense) about my own efforts to bring awareness to the forum members about the potential of aperture loss, but clearly, I am relieved that I have also included an urging for people to make their own measurements.

In your case, shortening further may not bring a noticeable improvement in performance, but it re-enforces my warning on these scopes (or at least perhaps the earlier versions) that one should be careful to avoid excessive back focus, and that to really know how an individual scope will behave, it is best to measure for one's self.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: Eddgie]
      #6146541 - 10/19/13 11:52 AM

I checked my aperture in reduction mode...it is...

175mm at infinity focus.

Will recheck straight thru measurement tonight.

My 8" Edge is 6 months old.


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HowardK
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Re: Final apeture reduction measurment for EdgeHD 8" new [Re: HowardK]
      #6155930 - 10/24/13 04:52 PM

For Eddgie

At infinity focus...Cliklok visual back.....35mm
WO 2" diagonal.......88mm
Power/filterswitch.....63mm
Mkv..........123mm

Total.....309mm

Aperture...
Reducer mode = 175mm
Straight thru = 186mm


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