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APM 0.75x 82mm Riccardi reducer not working

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#1 maxmir

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Posted 22 April 2020 - 12:47 PM

I can't get a flat field  APM 0.75x 82mm Riccardi reducer. I have been able to space the corrector +/- 5mm from the expected position in 1mm steps. I tested it over about 7 nights.

Corners still look bad.

Anyone had a defective reducer that had to go back?

 

Max



#2 Readerp

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Posted 22 April 2020 - 12:58 PM

Did you see an improvement in one direction or the other?

 

Perhaps 5mm is not enough?

 

I have a TSFlat3 flattener on my TMB 130,

and I had to move the focal plane 11.5mm closer than the stock adapter, when using my Nikon DSLR.



#3 Coconuts

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Posted 22 April 2020 - 02:09 PM

I own one of those, to use on a TMB 130 f/6 astrograph, but it is at a distant property, and I have yet to make or buy the adapter to mate it with my 3.5" FeatherTouch focuser.  So I can't vouch for its quality, other than to note that its designer is well respected, and that it is designed to fill a 52 mm imaging circle.  I've attached its nominal spot diagram out to 52 mm diameter.  The BFL info is detailed (also attached as an Excel spreadsheet), but it is also a bit confusing, so you might want to double check your spacing.  What scope are you pairing it with?  That matters a lot in setting the BFL.

 

All the best,

 

Kevin

 

Attached File  Apo 130_780+075x reducer.pdf   66.25KB   44 downloads

 

Attached File  Riccardi Reducer Info May 2014.xls   38KB   39 downloads


Edited by Coconuts, 22 April 2020 - 02:10 PM.


#4 StephenW

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Posted 22 April 2020 - 02:55 PM

I use one on my TMB 152mm F8 and have not had any issues.   I currently only have an STF-8300 mounted as the camera, so the small f.o.v is not challenging the reducer at all.  Will need to put a full frame camera on there to see how it really performs.

 

What system are you using it on and what spacing do you have set-up?



#5 chongo228

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Posted 22 April 2020 - 04:50 PM

I have the large and small Riccardi and both work....if your scope is really fast .5 could be too big of a jump in distance.



#6 juliangeorgeshaw

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Posted 27 April 2020 - 01:26 PM

I have the same problem.

 

I have a TMB 152mm F8 and a new ASI6200 full frame camera. Because it has a much larger diagonal (43.3mm) than my previous Atik460 I decided to use my APM 0.75x 82mm (large) Riccardi reducer for the first time.

 

The specified spacing is 70.6mm plus 1mm filter adjustment = 71.6mm. I found two methods for adjusting reducer spacing.  https://www.cloudyni...-2#entry9387717

 

Using the AstroPhysics method (matching focus in the center and at the corners) it seems I need an extra 4.5mm spacing. But with this spacing my stars in the corners are very elongated with the axis of elongation pointing towards the centre. According to the other method this means I should add more distance but moving to 7mm spacing made things even worse.



#7 maxmir

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Posted 19 May 2020 - 04:33 PM

I finally wrote Teleskope Service and asked for a replacement or refund.

They are contacting APM. 

I was able to use the baader M68 variable spacer to nail spacing to less than .2mm.

Unfortunately best spacing is 13 mm less than specified 78 mm back focus.

 

The stars show irregular shapes too ;probably combined coma and spherical aberrations.

 

 

There are not even nice ovals. 

 

Max



#8 maxmir

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Posted 19 May 2020 - 04:36 PM

I will post a image test soon.  I am using this with my AstroPhysics 130 F6 ( Pre grand turismo, Circa mid 1990s )



#9 chongo228

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Posted 19 May 2020 - 05:04 PM

If I remember correctly my 130 F6 and Riccardi spacing is at 77mm.

 

I've used 2 or 3 adjustable t2 spacers and found none of them to be worth the price. The best way I've found to adjust spacing is with one of  these.....These are not cheap but you don't have to disconnect anything.

 

https://www.teleskop...-not-twist.html

 

https://www.teleskop...connection.html

 

I have the T2 size one. It is adjustable from 18 to 28mm. I add some other spacers so the midpoint travel of the helical focuser will be at the target specified by the manufacture. Then I can adjust it easily at any interval I want and the camera or cords don't wrap up or need to be taken off. I use digital calipers to take a reading. Once I find my spacing I remove the helical and order/assemble the right size extensions to match. 

 

Hope that helps



#10 maxmir

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Posted 19 May 2020 - 05:33 PM

 I tested my M82 unit with 2 different cameras from different mfrs (ZWO and QHY 35mm sensors )

 

It should to be 77mm. The lens is correcting well short of this. Also, lots of residual aberrations at best spacing. 



#11 buckeyestargazer

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Posted 19 May 2020 - 06:10 PM

Can you share a pic of what you're seeing?

It sounds to me like one of the lens elements (of 3) got put in backwards.  



#12 Coconuts

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Posted 19 May 2020 - 07:49 PM

"It sounds to me like one of the lens elements (of 3) got put in backwards."

 

That should be pretty easy to check, here is a cross-section of the M82 0.75X large reducer:

 

Reducer 075X drawing.JPG

 

Another possibility is that two of the elements were swapped.

 

All the best,

 

Kevin



#13 maxmir

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Posted 19 May 2020 - 09:10 PM

This the best spacing and focus



#14 maxmir

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Posted 19 May 2020 - 09:11 PM

Image...

Attached Thumbnails

  • _15918_2_mosaic01.jpg


#15 maxmir

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Posted 19 May 2020 - 09:19 PM

The reducer is not backwards. I am using the FT 3.5 focuser adapter. The adapter insures correct orientation to fit inside the focuser.

I suspect the unit has element flipped inside as suggested. Hard to tell without taking it apart.

 

 

If you like stars to look like little birdies this the one to get :)

 

Max



#16 Jared

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Posted 19 May 2020 - 11:26 PM

I would have expected it to work OK with an AP130. For some reason, it is marketed as a reduced/flattener for all APM branded refractors. That simply isn’t possible. The amount of field curvature varies with the focal length of the refractor. As a result, the specified back focus won’t work with every refractor, so the amount of reduction will vary from one refractor to the next and the level of correction will also vary. That being said, your scope is not so much shorter in FL than the “average” APM refractor that I would have expected this much of a mismatch. Have others had better luck with this unit and 810mmfl refractors?



#17 maxmir

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Posted 20 May 2020 - 07:48 AM

Well I am screwed. Don't buy the Riccardi M82 for the AP 130 F6.

 

APM wrote me that this a oil spaced objective and the Riccardi reducer won't work properly .

I am trying to get a refund from Teleskope service center.

I am not sure they will since they said they want it to be brand new.

It is not brand new anymore. They should still refund in full. This is not my fault.

 

No warning in the APM or Teleskope web info.

 

Let the buyer beware.

 

Max

 

 



#18 buckeyestargazer

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Posted 20 May 2020 - 07:55 AM

Maxmir, what camera are you using?

Based on your image I'm not sure that there is anything wrong with the reducer.  It doesn't look "that bad" to me.  You mention in the original post that you moved the backfocus by 1mm increments.  Depending on your camera that may not be precise enough.  I am using a M82 Riccardi with my CFF135 f6.7 (oil spaced!) + ASI6200, and in trying to fine tune the backfocus I found that I needed to move it by just 0.25mm.  So I had to find some M68 0.3mm shims to get it right.  

 

Having said that, the stars do show some other small aberration that may or may not be due to correct backfocus.  


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#19 gatsbyiv

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Posted 20 May 2020 - 09:04 AM

Unless you buy a reducer that is specifically designed for your scope, there are always going to be compromises in performance.  No reducer can work perfectly for every scope due to design differences. APM at least lists a bunch of scopes they've tested it with and the optimal backfocus for each scope--that's a lot more detail that almost any other manufacturer I've seen provides.  For any scope not on their list, you're taking a chance, though.  You could try any of the other reducers that are out there and see if you get better results.  WO and Borg have (or at least used to) adjustable reducers that can be tuned to a specific focal length, but I don't think those will work with full frame sensors.  Full frame sensors are particularly demanding, so the corners of your image actually don't look that bad to me.  



#20 maxmir

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Posted 20 May 2020 - 11:07 AM

Are you guys kidding me? Look at images carefully.

 

My Nikon 14-28mm wide angle camera lens has better full frame correction than this and it not made for AP.

I be testing this the ASI 6200 and the QHY128C.

 

I am able to make continuous sub mm adjustments with a Baader M68 15-20mm Vari-adapter.

After over and half hour of fine adjustments, I gave up



#21 maxmir

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Posted 20 May 2020 - 11:21 AM

Really, You guys you would gladly pay 500.00 + 250 adapters for a poor performing optic?

 

Then have the manufacture to now tell you it will never work anyway?

They could have suggested that it would not work in the literature.



#22 StephenW

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Posted 20 May 2020 - 01:45 PM

You mentioned that this is an earlier model AP (mid '90s) so just curious how do your images look on full-frame without the Riccardi in place?  i.e. How much base aberration is inherent in the scope that you are looking for the Riccardi to correct?   And did you contact AP to see what they recommend for full-frame reducers with this scope?

 

My interaction with APM was very positive - I contacted them before buying the M82 for my TMB to check it would work well, what the spacing should be etc and they were very helpful.

 

Hopefully you get this sorted out!



#23 maxmir

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Posted 21 May 2020 - 12:07 AM

I am dealing with Teleskope Service. They are relaying info from APM.

I am very disappointed in TS. They not offering a full refund on the reducer.  

Caveat emptor, YMMV

 

Max



#24 Jared

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Posted 21 May 2020 - 01:44 AM

Honestly, the response doesn’t make much sense to me. Why would an oil spaced refractor not work? Generally speaking, the radius of curvature for any doublet or triplet refractor is about ⅓ of the focal length. So all refractors of a given focal length should need essentially the same flattener. That’s why, for example, my AP 105mm Traveler from 1994 (oiled) and a current AP 92mm Stowaway (Air spaces) share the same flatteners and reducers. They have the same focal length.

APM, it sounds like, is trying to use the same reducer/flattener for a large number of telescopes of different focal lengths by varying the back focus. This will, of course, change the amount of focal reduction, but OK. If they have given the correct back spacing for another refractor of the same focal length as your 130, I would have expected that to work reasonably well for ANY refractor of that focal length. Obviously, any given reducer/flattener is designed for one specific radius of curvature, so it will only be perfect at that one focal length.

#25 maxmir

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Posted 21 May 2020 - 07:31 AM

Honestly, the response doesn’t make much sense to me. Why would an oil spaced refractor not work? Generally speaking, the radius of curvature for any doublet or triplet refractor is about ⅓ of the focal length. So all refractors of a given focal length should need essentially the same flattener. That’s why, for example, my AP 105mm Traveler from 1994 (oiled) and a current AP 92mm Stowaway (Air spaces) share the same flatteners and reducers. They have the same focal length.

APM, it sounds like, is trying to use the same reducer/flattener for a large number of telescopes of different focal lengths by varying the back focus. This will, of course, change the amount of focal reduction, but OK. If they have given the correct back spacing for another refractor of the same focal length as your 130, I would have expected that to work reasonably well for ANY refractor of that focal length. Obviously, any given reducer/flattener is designed for one specific radius of curvature, so it will only be perfect at that one focal length.

I agree it makes no sense at all to me either. I have been in the hobby since age 12 and imaging since 1998.

Most APO designs are minimizing spherochromatic aberrations on and off axis. Roland's Christen's designs have been the gold standard since the early 1990s.

 

APMs info on the Riccardi M82 show nice spot diagrams tests with a no name Chinese apo doublet.

I think the correction on most well designed APO triplets would be much better.

 

TS tells me APM is not willing to credit them for the corrector.

So ultimately APM is ducting their obligations on this product.




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