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Do universal focal reducers exist?

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#1 stars n planets

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Posted 11 March 2020 - 08:40 AM

Ok. So not completely universal as thread types vary.

I have an Altair 60mm triplet which at 420mm FL makes it F7 which i want to reduce.

Can i get one which works on any other refractors?

#2 stars n planets

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Posted 11 March 2020 - 09:54 AM

A 0.8 reducer bring it down from F7 to F5.6 will this be big difference??

#3 jseivert

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Posted 11 March 2020 - 10:03 AM

I have a William Optics P-Flat-4 that is a .8 variable reducer/flattener.  You can adjust it instead of having to use spacers to get the right distance.  Works great on my 110mm  f/6 refractor



#4 stars n planets

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Posted 11 March 2020 - 10:05 AM

I have a William Optics P-Flat-4 that is a .8 variable reducer/flattener. You can adjust it instead of having to use spacers to get the right distance. Works great on my 110mm f/6 refractor


And what refractor is it on? William optics?

#5 Gipht

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Posted 11 March 2020 - 10:34 AM

Many telescope optics require reducers/flatteners that match up with optics of the telescope.   If I  try and use my Stellarvue reducer/flattener on my ES 127 AR, the results are terrible.  The ES 127AR optics are reasonably flat as is, and the reducers/flattener  corrects for curvature that is not there.

 

I would contact your telescope manufacturer and see if they will recommend a  product.  Keep  in mind that most reducers/flatteners  are not perfect.



#6 sg6

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Posted 11 March 2020 - 10:38 AM

What thread is on the Altair?

You can get I think - only think - thread converters from Precision parts.

So find yours, find the WO and get a converter.



#7 YAOG

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Posted 11 March 2020 - 10:45 PM

Ok. So not completely universal as thread types vary.

I have an Altair 60mm triplet which at 420mm FL makes it F7 which i want to reduce.

Can i get one which works on any other refractors?

Optically like most things for best results you need a reducer flattener that is designed to be used with an optic similar to your scope. There are trade offs and you may not get as large a corrected field or some other compromise. But generally speaking yes this is doable if you look for reducer flatteners that are designed to be used this way. TS Optics has many combinations figured out for you. Look on their website for advice and appropriate back spacing for your optics. 

 

Starizona has a pair of very impressive ED apo reducers that should work for you, there are two versions pick the one for the focal length of your scope and off you go. 



#8 Jon Isaacs

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Posted 12 March 2020 - 04:43 AM

Field curvature is primarily a function of focal length so ideally, a reducer/flattener is designed for a small range of focal lengths.

 

Jon


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#9 GOLGO13

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Posted 12 March 2020 - 10:51 AM

I use a .7 Antares reducer (it screws on a 2 inch diagonal or 2 inch to 1.25 adapter). It works well for my purposes (night vision). I have a .5 GSO one also, but it doesn't seem to be as good in usage from what I can tell.

 

However, I don't think it flattens anything, so that would be the negative depending on your situation. But for NV it works quite well.



#10 YAOG

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Posted 12 March 2020 - 11:31 AM

I use a .7 Antares reducer (it screws on a 2 inch diagonal or 2 inch to 1.25 adapter). It works well for my purposes (night vision). I have a .5 GSO one also, but it doesn't seem to be as good in usage from what I can tell.

 

However, I don't think it flattens anything, so that would be the negative depending on your situation. But for NV it works quite well.

I think for NV use with typically narrow 40 degree FOV and low resolution it is less of a issue and most anything will work. 


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#11 YAOG

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Posted 12 March 2020 - 11:32 AM

Ok. So not completely universal as thread types vary.

I have an Altair 60mm triplet which at 420mm FL makes it F7 which i want to reduce.

Can i get one which works on any other refractors?

Just look for anything designed for an f/7 400-500mm f/l and once you work out the spacing you'll be fine. 

 

This one will work for you: TSRed279 see the chart, use a 65mm back spacing and you are GTG. 

 


Edited by YAOG, 12 March 2020 - 11:40 AM.


#12 stars n planets

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Posted 13 March 2020 - 05:18 AM

Just look for anything designed for an f/7 400-500mm f/l and once you work out the spacing you'll be fine.

This one will work for you: TSRed279 see the chart, use a 65mm back spacing and you are GTG.


Would a 0.8 reducer be too aggressive causing to much curvature?

#13 YAOG

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Posted 13 March 2020 - 09:11 AM

Would a 0.8 reducer be too aggressive causing to much curvature?

I think you may be mixing up terms. Field curvature is just that the image plane where the image comes into focus is not flat but curved. Usually the focal plane curvature is similar in shape to the lenses forming the image. 

 

Most reducers are designed to reduce the image and to flatten the field curvature at the same time. This is why most reducer/flatteners require specify a fixed distance from the back element to put the image sensor or your eyeball. Most reducer/flatteners can accommodate some variation to adjust the field curvature which also changes the image reduction slightly. But because field curvature is visible in an image as blur normally people choose to adjust back focus to correct for the blue caused by curvature. 

 

There are some reducers being produced now that do not have a flattener component to their optical function.These special purpose reducers can be used with telescopes that have been designed to produce images with flat fields. Scopes like most Petzval quads or similar symmetrical designs or triplets designed with an extra lens group to flatten the image but these are usually designed for imaging. 

 

But the vast majority of lenses need flatteners. 



#14 JohnPancoast

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Posted 13 March 2020 - 09:27 PM

And what refractor is it on? William optics?

I have the same question... I have a WO 110 Megrez and have struggled to get this to work with an OAG. Probably operator error...confused1.gif



#15 YAOG

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Posted 14 March 2020 - 12:29 AM

I have the same question... I have a WO 110 Megrez and have struggled to get this to work with an OAG. Probably operator error...confused1.gif

Why struggle with an OAG for a small refractor? Piggybacked is much better and offers much easier setup and guiding. 


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#16 Jaimo!

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Posted 14 March 2020 - 03:51 PM

I am currently using a new WO-Z81 with their Flat6AIII reducer/flattener, it is adjustable for a number of the William Optic doublets and triplets.  I have ordered an adapter so the Flat6AIII can fit into a 2" focuser and I am planning to trying it out in the AT102ED f/7...  I cannot think of a reason it is not worth trying.



#17 JohnPancoast

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Posted 15 March 2020 - 02:17 PM

Why struggle with an OAG for a small refractor? Piggybacked is much better and offers much easier setup and guiding. 

Right. Only because I have been guiding with an OAG since I began, and don't gave a finder scope. Easily solved if I can't make it work. smile.gif



#18 YAOG

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Posted 15 March 2020 - 08:12 PM

Right. Only because I have been guiding with an OAG since I began, and don't gave a finder scope. Easily solved if I can't make it work. smile.gif

So you are plate solving to get on target? What is not making the OAG happy? With a WO110 MegRez it seems like you are going to be very undersampled with a ASI071 even without a reducer unless your seeing is typically what I'd call not very good. 



#19 JohnPancoast

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Posted 16 March 2020 - 10:20 AM

YOAG, I've been doing this for a few years, but lucky to do AP on more than 8 or 10 occasions per year, usually in reasonably dark sites that my club uses in the Washington DC suburbs. I find myself to be re-learning something every time I go out!

 

I do not plate solve. I polar align with Polemaster and star align through the camera to known stars.  I focus on a star, then  slew to my target and take sample frames to get proper framing. My problem with the OAG was getting to focus, but I may just need to work harder to get the backfocus correct.

 

On the undersampling, your comment got me thinking.

 

Until last summer, I was using a modified DSLR with the WO110, which I bought originally for visual. I replaced the DSLR with the ASI071 to get the cooling I wanted (Wow, what a difference!)

 

I don't know how to measure seeing, but with electronic focusing (FWHM) on stars, I rarely get below about 3.0, which I assume refers to arc seconds (but I really am not sure about that.)

 

My WO110 (655mm f/l) with the ASI071 should give me 1.5 arc seconds per pixel.

 

WIth these in mind, what camera would you think is better suited to the William Optics 110?

Conversely, what type of scope would you think is better suited to the ASI071?



#20 YAOG

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Posted 16 March 2020 - 12:21 PM

YOAG, I've been doing this for a few years, but lucky to do AP on more than 8 or 10 occasions per year, usually in reasonably dark sites that my club uses in the Washington DC suburbs. I find myself to be re-learning something every time I go out!

 

I do not plate solve. I polar align with Polemaster and star align through the camera to known stars.  I focus on a star, then  slew to my target and take sample frames to get proper framing. My problem with the OAG was getting to focus, but I may just need to work harder to get the backfocus correct.

 

On the undersampling, your comment got me thinking.

 

Until last summer, I was using a modified DSLR with the WO110, which I bought originally for visual. I replaced the DSLR with the ASI071 to get the cooling I wanted (Wow, what a difference!)

 

I don't know how to measure seeing, but with electronic focusing (FWHM) on stars, I rarely get below about 3.0, which I assume refers to arc seconds (but I really am not sure about that.)

 

My WO110 (655mm f/l) with the ASI071 should give me 1.5 arc seconds per pixel.

 

WIth these in mind, what camera would you think is better suited to the William Optics 110?

Conversely, what type of scope would you think is better suited to the ASI071?

Hi John,

 

Okay with kinda not so good seeing you seem to have I think you are correct and your pixel pitch should be fine. We must have better skies here out west I guess at our dark sky site. 

 

If you ever get to a site with steadier air and good transparency you might consider using a camera with smaller photosites like the 183 based cameras. If you combine the smaller format sensor camera with a reducer flattener you can often get similar FOV but much higher resolution and shorter times mostly from the much more sensitive 183 sensor. Then you need to really get your mount autoguiding perfectly to get most from the smaller pixels. 



#21 JohnPancoast

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Posted 07 April 2020 - 07:12 PM

Yoag,

 

Thinking about your comment re: undersampling.  I wonder if I could accomplish better outcome by adding a TeleVue 2X PowerMate to the imaging setup? Might get closer to 1.5 arc-sec per pixel.

 

John



#22 YAOG

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Posted 07 April 2020 - 07:42 PM

Yoag,

 

Thinking about your comment re: undersampling.  I wonder if I could accomplish better outcome by adding a TeleVue 2X PowerMate to the imaging setup? Might get closer to 1.5 arc-sec per pixel.

 

John

Hi John,

 

Of course it works both ways! One of the techniques the best planetary imagers use is to pick a smaller sized sensor chip for the super fast frame rates they can produce and then play with f/ratio to get the right pixel/pitch per arc second. A C14 seems like a good planetary scope but when you realize how tiny the planets are you have to oversample to get as many pixels as possible and to overcome the atmosphere messing up your images. By imaging at high speeds you are freezing the image like using a fast shutter speed to capture motion. By capturing images in between the disturbed air and cherry picking only the best of many frames and stacking them you can get amazingly good, detailed images of tiny objects. So a C14 with a 2x PowerMate and an ASI178 camera with giant 5.86um photosites can capture something like 0.15" per pixel. Using the same camera with a C11 you need to use a 3X amplifier to match the C14's resolution. This might sound crazy until you do the math and realize that Nyquist was an optimist.  

 

So to answer your question yes, playing with the focal ratios is a perfectly valid way to gain control over pixel/pitch per arc second. But also realize using a PM or other amplifier will reduce the chip's FOV.  


Edited by YAOG, 07 April 2020 - 07:47 PM.


#23 Jeff B

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Posted 08 April 2020 - 09:20 AM

Stars n Planets, Is this for photography or visual?



#24 stars n planets

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Posted 08 April 2020 - 09:58 AM

Stars n Planets, Is this for photography or visual?


It is for astrophotography.


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