Final apeture reduction measurment for EdgeHD 8"
Posted 14 October 2013 - 01:07 PM
Posted 14 October 2013 - 04:28 PM
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.
Posted 14 October 2013 - 04:52 PM
Clear skies to you
Posted 14 October 2013 - 05:03 PM
I also get a lot out of Eddgie's posts on all forums he is at large on.
Very knowledgeable and prolific
Posted 15 October 2013 - 07:19 AM
Posted 15 October 2013 - 08:46 AM
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
Posted 15 October 2013 - 11:06 AM
Posted 15 October 2013 - 11:47 AM
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.
Posted 16 October 2013 - 03:36 PM
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?
Posted 16 October 2013 - 04:19 PM
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.
Posted 16 October 2013 - 04:22 PM
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...
Posted 16 October 2013 - 04:27 PM
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.
Posted 16 October 2013 - 05:05 PM
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.
Posted 16 October 2013 - 05:26 PM
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
Posted 16 October 2013 - 06:04 PM
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..
Posted 16 October 2013 - 06:18 PM
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...
Posted 16 October 2013 - 06:38 PM
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...
Posted 16 October 2013 - 07:05 PM
I wonder where the field stop of the Denk eyepieces is compared to others?
Posted 16 October 2013 - 08:31 PM
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.
Posted 17 October 2013 - 04:16 AM
Cliklok visual back.....35mm
WO 2" diagonal.......88mm
I use 16mm NAGLERS pretty much all the time.
Loooong light path eh?
Posted 17 October 2013 - 08:42 AM
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....
Posted 17 October 2013 - 09:47 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.
Posted 17 October 2013 - 11:29 AM
I am going to recheck my aperture measurements again in reduction mode and straight thru
Just to be certain
Posted 17 October 2013 - 06:53 PM
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.