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Binoviewers for a C8 HD

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#1 pjensen

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Posted 30 April 2013 - 01:35 PM

Been looking at the Baader Maxbright and wondering which diagonal to use with it.

The telescope is a C8 Edge with a 1.25" visual back. What exactly is needed? With all the options, it is a little confusing.

Thanks,

Paul

#2 REC

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Posted 30 April 2013 - 02:02 PM

Hi Paul, that would be a good choice of a BV to get started and have read they are the best in that price range. There is a guy on this forum that is an expert on these named Eddgie and I'm sure he will guide you.

BV in a SCT is pretty easy and will focus ok without adding all kinds of extra stuff, for lack of a better term.

Have fun!

Bob

#3 Eddgie

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Posted 30 April 2013 - 03:27 PM

Hello Paul,

If you have not been on this forum before, then you would not have seen it, but I recently did some testing on the EdgeHD 8".

There is one issue with binoviewers on the EdgeHD 8" that you need to be aware of.

The EdgeHD seems to be a bit different in the amount of back focus it can tolerate before the system starts to loose apeture.

The very long light path of binoviewers means that in order to reach focus (and reaching focus is not a problem mechanically) means the the primary miror moves pretty far forward when you turn the focuser knob enough to reach focus with binoviewers.

As it does this, the outside of the light cone will start to be shaved off by the baffles in the telescope.

The result is that the system looses apeture.

If you decide to binoview (and I do recommend binoviewing in general) then for the EdgeHD 8" (and SCTs in general) it may be desirable to spend the extra money on a binoviewer system with the shortest possible light path.

And notice that I said "System" vs binoviewer.

Since Binoviewers use prisms and a splitter, just like the SCT, the light path of a binviewr is "Folded."

This means that the distance the light travels inside the binoviewer is longer than you would think.

Most diagonals have an eyepeice holder, and the nose on the binoviewer is then inserted into the holder. The problem though is that the eyepeiece holder is usually about 30mm.

Finally, you need to connect the binoviwer to the visual back of your scope. The probelm with the 1.25" visual back is that it is very long (maybe 45mm of light path).

Now when you add these three componenets together ( 40mm + 30mm + 110mm) you wind up with a light path of 180mm

Not the problem with this configuration in the EdgeHD is that this is going to cut your aperture to 7.5 inces or so.

Now to be fair, this is only about an 18% light drop, but remeber that the central obstruction stays fixed, so as a percentage of apeture, since the apture gets smaller, the percentage of apeture grows.

In the end, this means that you have a scope that 1s working as a 7.5" scope with 2350mm of focal lenght and a 37% obstruction.

Now to be fair, a lot of people may not be able to see the damage that this does. I could see it easily when observing planets. Even when using 15mm eyepcies (and allowing for the focal lenght increase) I found planets to start to look very dim. Deep sky also seemed not quite as brigth, though clusters still look lovely.

So, what can you do?

Again, I recommend binoviewrs, but you may want to look at a system approach that allows you to shorten the light path as much as possible.

Very specifically, here are the components I recommend.

The first is the Baader SCT to T thread adapter with a light path of 15mm (this is whay I am using now).

Baader SCT to T2 15mm Adapter

Nest, I recommend the Baader T2 standard Prism diagonal. This diagonal has a light path that is only 38mm. This is about as short as you can get. This is the one I use:

Baader standard T2 Prism. middle of the page

You already have the Maxbright, so you are set to go with the above.

This configuraiton will come out with to (15mm + 38mm + 110mm) to 163mm. Now even at this, you may still not be working at quite full apeture, but you should be very close.

I use the same configuration but I use Mark V binoviewrs and these have a 13mm longer light path.

I measured the apeture with this configuration and a couple of others, and figured that every 11mm of back focus you can shave off should ad .1" to the apeture.

My current configuration would be 13mm longer than the one above, and when I measured it, I measured 7.8" of apeture (and this was down from 7.5" when I first started shortening the light path).

So, if 11mm buys .1 inch, you should be at 7.9 inches of apeture.

And the GPC is there for when you want to do planets. Using the GPC, you should get another .1" for the full 8" of apeture, though to be honest, on one will see the difference between 7.9" and 8" of aperture.

Now this is not all that inexpensive, but in the end, the Baader stuff is very high quality, and this system will give you the brightst views you can get when using a binoviwer in the EdgeHD 8".

If you want to get the most from your EdgeHD 8" though, even if you have to save some, I highly recommend the configuration above.

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#4 Eddgie

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Posted 30 April 2013 - 03:36 PM

By the way, if you made it this far, there is one other option.

There is also a 10mm adapter. The problem with the 15mm adapter is that like the old SCT diagonals, you have to loosend the collar to rotate the diagonal.

The 10mm Adapter threads to the diagonal but does not allow for rotation.

To get the thing to rotate and be easier to lock into position, there is a lock wheel that you can use.

I may go to this setup myself. Here is a page that shows how it works, but you can do this with the T2 Prism and the 10mm SCT adapter as well...

Mounting a Baader diagonal directly to the SCT using the SCT lock ring.

#5 Eddgie

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Posted 30 April 2013 - 03:37 PM

And the prism is the standard prism, not the far more expensice Ziess prism. I think the standard prism is quite excellent, and there is no need to spend twice as much.

#6 Eddgie

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Posted 30 April 2013 - 03:58 PM

One last option, then I will shut up... LOL.

I think that keeping the light path on an SCT as short as possible is also beneficial for even general use because it keeps the system from gaining a lot of focal lenth.

The above otions are not very convenient, and there is an "convenience" option that I sould mention.

This is to use the Baader with the Televue Short SCT 2" adapter.

This is 30mm of light path (vs 15mm for the SCT to T2 connector), but if you have a diagonal with a short nose, this makes it a snap to change back and forth, but still keeps the back focus to a minium.

I actually use a chop saw to cut one of my diagonals so that it would fully seat, but the standard Baader 2" nose works great.

Again, maybe 10mm to 15mm shorter than most standard SCT to 2" adapters but .1 inch less apeture than the 15mm Adapter.

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#7 pjensen

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Posted 30 April 2013 - 07:20 PM

The above otions are not very convenient, and there is an "convenience" option that I sould mention.

This is to use the Baader with the Televue Short SCT 2" adapter.


Eddigie, thanks for your exhaustive analysis on this issue. That is exactly what I needed (to buy the right stuff).

I had read several of your posts before and was worried I couldn't use a binoviewer on this scope.

Thanks for your help.

Paul

#8 orion61

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Posted 30 April 2013 - 10:15 PM

If you have never tried a BinoViewer before, a decent cheap one is the Arcturus for $119.00 self centering ocular collars
and included nose piece. It gave me the best view I have ever had of Jupiter, there was so much detail I was overwhelmed.
Another thought on the 7.5 VS 8" is the fact that usually
if a mirror has a bad area it is usually the edge.
In some cases I could actually see it helping you out.
I have learned my lesson about making too big of a deal on CO's just look at the RCX Meades, that thing is HUGE but every one I have looked through has been SUPER sharp.
Collimation not being an issue.. Which was the main flaw in them and the front of the assembly moving for focusing.
I have looked into some very expensive (and beautiful) binocular viewers and was exceedingly happy with what I saw in the comparing images!
If you have the extra $$ great...

#9 REC

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Posted 01 May 2013 - 07:20 AM

Also on the cheap to test the waters is the WO complete set w/EP"s for $200. You can turn them in no time for $180 and then step up to the more expensive units if you get hooked!

#10 Eddgie

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Posted 01 May 2013 - 08:08 AM

I am going to publicly recant my recommendation for the SCT 15mm to T-thread adpater.

Last night when I was observing using my binoviewer in the EdgeHD 8", even with the collar tight, the diagonal suddenly rotated 180 degrees. Fortunaltly for me, I had the eyepeices in tight.

I was using heavy Hyperions, so this was an aggrevating factor, but it has happened before, and I won't let it happen again.

I would go with the Televue Short SCT to 2" and the 2" nose, with a 2" short nose diagonal (cut one if you need to) if you want to make it easy to change, or the 10mm SCT to T2 adapter and the Lock Ring.

Nothing scares me more than the thought of dumping a pair of expensive eyepieces on to the ground because the diagonal broke free.

Also be aware that there is a hole in the side of the rings that screw into the nose of the diaginoal. These are to allow you to use the end of a hex key as a prybar so you can make sure that when you put the 15mm Adapter on to the diagnal, you can get that puppy on tight.

Anyway, I can no longer recommend the 15mm SCT to T2 connector. If there is clearance for the lock ring (I think there is on the EdgeHD 8", but not the C5) then this would be the way to go if you want to stay as bright as possible.

But if you are going to go back and forth between binoviewers and monoviewing (and I do less and less of this these days), then the Televue Short adapter (with a diagonal with short nose, and they are easy to cut, but you loose filter threads) and 2" nose may be the best compromise.

#11 SteveSMS

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Posted 01 May 2013 - 08:20 AM

Hi Paul,

I've been having a great with my EdgeHD 8 and a pair of TV Binovues. I have a Baader Click-Lock 2" SCT VB on the scope and I use a 2" to 1.25" Baader Click-Lock with a GSO dielectric 1.25" diagonal. I use the 2X OCA with the Binovue and I have had great success with EPs from 15mm to 40mm. I can't say enough about the Click-Lock, it is one of the best astro accessories that I have ever used. Once you start using binoviewers in your Edge you will most likely be sorry you didn't do it sooner!

Clear Skies,

Steve

#12 hfjacinto

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Posted 01 May 2013 - 09:55 AM

I second the Baader Click lock and the MaxBrights are awesome.

#13 coutleef

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Posted 08 May 2013 - 07:49 AM

I second the Baader Click lock and the MaxBrights are awesome.


i agree so much as well. i just bougth one and it makes life so easy and secure. i will measure the loss of aperture mentionned by edgiee tonogth and will report what happens with a click lock VB plus 2 inch WO diagonal plus WO bino. i compared using the 2 inch diagonal versus a 1.25 inch diagonal in this confoguration and saw no difference on saturn. but i used the stock diagonal that came with my 8 se that is not of very good quality

#14 Eddgie

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Posted 08 May 2013 - 09:17 AM

Please do. I am eager to see.

My estimate is that the aperture will be reduced to about 7.1 inches. The focal lenght will be about 2400mm.

Really curious to see the number though.

Personally I think this is the wrong approach, but you are the one that has to be pleased, not me.

#15 coutleef

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Posted 08 May 2013 - 09:37 AM

Please do. I am eager to see.

My estimate is that the aperture will be reduced to about 7.1 inches. The focal lenght will be about 2400mm.

Really curious to see the number though.

Personally I think this is the wrong approach, but you are the one that has to be pleased, not me.


i just want to be sure that going to a 1.25 inch diagonal will make a significant change justifying this investment.

#16 coutleef

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Posted 08 May 2013 - 07:39 PM

Please do. I am eager to see.

My estimate is that the aperture will be reduced to about 7.1 inches. The focal lenght will be about 2400mm.

Really curious to see the number though.

Personally I think this is the wrong approach, but you are the one that has to be pleased, not me.


Dear eddgie,

You may be disapointed. I did the experiment, i focused the bino on saturn, kept the focus knob at that place and then took the scope inside and flashed a red light through the eyepiece at one foot of the wall in the dark

Much easier than i thougth.

With a WO bino, a 2inch WO diagonal and baader clicklock VB, i obtained a circle of 7.5 inch.

Now i am hesitating to buy a new 1.25 inch diagonal. Maybe that could bring the effective aperture to 7.8??

Will that be worth it??

#17 Eddgie

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Posted 08 May 2013 - 09:40 PM

I am not at all disappointed for you..

I have a much shorter light path. 30mm Visual back, 38mm diagonal, and 123mm in the binoviewer, and my aperture was only 7.6 inchs.

When I shortened it up from the Clicklock to the 15mm Baader, I got only 7.7" or about 1/10th inch for each 11mm of back focus I cut off.

Maybe there is something on my particular scope that is causing the difference. Maybe my baffle is a bit longer or something.

I thought that it was kind of tight to start with. In my case, it would indicate that the scope is loosing aperture with about 160mm of back focus.

So, happy that yours is not affected more.

But now is the question. If there is something different from my scope, it could be that by shortening up, you could come very close to getting full aperture, or perhaps even get full aperture.

It doesn't look like my scope would have full aperture even if I shortened it to the 10mm Baader connector.

So, not sure if there is some difference in the scope, but it sounds like you might actually be able to get full aperture if you were to shorten up a lot.

It is only worth it if it is worth it to you though.

#18 coutleef

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Posted 09 May 2013 - 08:08 AM

thanks for the great advice

on second thought improvement will come also from a better quality diagonal compared to the stock celestron 1.25 inch diagonal i used. bu increasing aperture to 7.8 inch with the 1.25 inch diagonal and improving the views with a better diagonal, these rather modest changes may result in better views.

i think i will get an astrotech diagonal 1.25 inch

#19 Eddgie

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Posted 09 May 2013 - 08:30 AM

Remember, there are several benefits to shortening the light path.

First and most obvious is that 7.6" will only be about 12% brighter. Now on most targets this will be difficult to see, but every little bit helps.

There is also the slight loss of contrast due to the larger obstruction. Again, every little bit helps.

Finally, there is the true field size. Since the current configuration is causing your scope to work at maybe 2450mm, shortening this down quite a bit could give you a bit more true field.

Once again, every little bit helps.

But improving all of these together simply may not be worth it unless you were to try to improve them in a "Big" way.

My advice would be to consider spending more and getting the Siebert diagonal.

Look at his site for Ad #1C

Again, this diagonal is going to cost you more, but with it, rather than going to 7.7", you may in fact go to 8", and this will mean that youer scope is alwo going to be something like 2200mm rather than 2450mm.

To me, spening a little for a tiny improvement is not nearly as good an idea as spending maybe double for double the improvement.

$169 is not cheap, but considering that you bougth an EdgeHD 8" over a standard C8, one would think that these differences were enough to be worth the difference in price.

Good luck with your decision.

#20 coutleef

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Posted 09 May 2013 - 09:28 AM

sorry if i have mistaken you but i habe a standard 8se not an edge SCT.

i will look at the siebert

#21 Eddgie

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Posted 09 May 2013 - 09:41 AM

Ah, well that explains the difference as to why you did not see the same amount of apterure loss that I did.

For some reason, I missed that you were using a standard C8. I guess because this was a thread about binoviewing the EdgeHD 8", I must have jumped to the conclusion that you were also using an EdgeHD.

And that figure (7.6) is about exactly right for the standard C8.

Assuming 230mm of back focus (just a guess) your apeture would indeed be 7.6" or so.

My apologies for my confusion.

If you are using a standerd C8, assuming that the light path would be Clicklock (38mm of back focus) Siebert Diagonal (about 45mm of back focus) and WO binos (about 110mm of back focus, the would put you at about 190mm to 200mm of back focus.

With 200mm of back focus, you should be working at about 7.9", but you would also reduce your focal lenght quite a bit as well.

Again, forgime my confusion.

#22 beammeup

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Posted 09 June 2013 - 05:35 PM

I have the recommended Eddgie setup for my c8 hd (with Maxbright binoviewer) and two Baader hyperion 17mm eyepieces.
My question is: should I also use the 1.25x Glass Path Corrector?
Will I lose aperture/brightness?
Also where should it be positioned (position A or B?).
I did read somewhere that it might be better positioned nearest the optical tube (position B in the picture)



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#23 Eddgie

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Posted 09 June 2013 - 07:42 PM

There would not be that much benefit in the GPC for general viewing, but for planets where you want as much aperture as possible, I would put the GPC in between the nose and the front of the diagonal. This will give you about 1.5x but it will increase the aperture by maybe 2 tenths of an inch.

What visual back are you using?

if you are using the Televue Shorty/T2/Maxbrights, you are probably already working at 7.7" and the 1.25" GPC will be like shortening the light path about 20mm, and this will give you very close to full aperture.

For general viewing though, it restricts your exit pupil to much. It is better to have the much lower power vs the slightly larger aperture because for most deep sky observing, you want the ability get as low a power as possible.






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