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Focal reducer on a Mak to lower focal ratio?

Maksutov
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#1 Cziffra

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Posted 09 June 2020 - 12:05 PM

I know Mak's aren't ideal for AP because they have high focal ratios. But could I attach a reducer to mitigate this? Many use the .6 on SCT's, but I never read of them being used on Maks. Would a reducer not work on a Mak?



#2 Shorty Barlow

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Posted 09 June 2020 - 12:19 PM

I don't think many Mak's have the visual back for a reducer, but I could be wrong.



#3 petert913

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Posted 09 June 2020 - 12:19 PM

Should work fine. Light waves are light waves. 



#4 vtornado

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Posted 09 June 2020 - 01:25 PM

You need to buy and adapter I think from scopestuff to convert the rear port of the mct to take the .63 sct focal reducer.

Check this thread out for similar discussion.

https://www.cloudyni...tion-questions/


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#5 Hesiod

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Posted 09 June 2020 - 02:00 PM

Smaller ones will have horrible vignetting; also, they could become somewhat faster, but will be nonetheless very slow (likely in the f/8-f/10 range, assuming a native focal ratio between f/15 and f/12; going from f/8 to f/6 almost halves the exposure...).
If already own a 6-7" MCT, and if deem worth the attempt, may get the FR: it is not outrageously expensive and probably can find one used, to be sold again if the experiment fails.

#6 KLWalsh

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Posted 09 June 2020 - 03:52 PM

Maks can be used for imaging. My Ioptron Rumak is f/12.
Though, coincidentally, I recently ordered the items to try imaging at f/7.56.
 

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#7 photoracer18

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Posted 09 June 2020 - 04:45 PM

The Intes focal reducer for the Maks with moving primaries is 0.6x. The Intes Maks have Celestron SCT rear threads.


Edited by photoracer18, 09 June 2020 - 04:54 PM.

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#8 luxo II

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Posted 09 June 2020 - 07:51 PM

I have a 0.5X reducer which screws into the camera adapters, they seem to work well enough with a smallish sensor camera like the ZWO-ASI533 (11 x 11mm) on the MK66 and M615, giving about f/6 and f/8 respectively. To use it on my APM mak (fixed mirrors) I'll have to adjust the primary mirror separation as the crayford doesn't have enough travel.


Edited by luxo II, 09 June 2020 - 07:56 PM.


#9 mtc

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Posted 09 June 2020 - 08:10 PM

I have the adapter mentioned above and an f.63 fr on my 5" mak - works fine for me. I leave it on all the time for viewing and imaging.

#10 Eddgie

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Posted 13 June 2020 - 04:25 PM

A great deal would depend on the telescope itself and in particular if it is an MCT that uses a moving primary to focus.

 

The MCT is usually compromised for visual use and this means that the designer can allow a very small fully illuminated field of view.  Typically SCTs and MCTs only really fully illuminate a very small circle, outside of which the field is vignetted by the front opening in the primary baffle.  

 

Now two things happen when you use a reducer. The first is that the fully illuminted field is reduced in size by the power of the reducer.  For example, if the fully illuminated field is 6mm without the reducer and you put a .5x reducer on it, the fully illuminated field will be reduced to 3mm.  Now that is not that big a deal.  A planet at the center of the field will still be seen as 100% illuminated and will still be presented at the resolution of the full aperture.   Outside of this 3mm circle though, the field is slightly reduced in brightness and the contrast and resolution is slightly lowered, and the further you get away from the center of the field, the more this occurs.  Remember, this is true even without the focal reducer, but now you have made everything happen at half the distance than it took before.

 

By itself that would be pretty inconsequential for visual use (though the vignetting might show in wide field images.)

The second thing that can happen though is that to get the working distance for the reducer, if the mirror spacing has to be changed very much, depending on the scope design, you could have a situation where the baffle starts to clip off the axial rays and at this point, the scope is in a reduced aperture configuration.  Now that does not make the scope unusable, it just lower's its performance.  

 

The only way to know for sure (unless you have a ray trace) is to measure the aperture using the laser projection method.  Once you know if there is aperture reduction, or if so, how much aperture is being lost, you can make a better decision about how you feel about it.

 

Of you could just get a reducer and use it and ignore all of this.  If you like the result, then nothing else matters. 



#11 kathyastro

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Posted 13 June 2020 - 05:18 PM

I have used a standard Antares 0.63 reducer on my orange tube C90.  It brings it down to f/7.  There could be some vignetting, but it wasn’t really objectionable.

 

In order to make it fit, I used an ETX to SCT adapter.



#12 deepwoods1

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Posted 13 June 2020 - 05:30 PM

I’ve used a Celestron .63 on a more recent Orion 150Mak without visual issue. 



#13 Hesiod

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Posted 13 June 2020 - 05:52 PM

The main point is however that most MCTs will be still painfully slow even with the focal reducer, and that is a reason good enough to opt for a SCT if the purpose is deep sky AP.

Intes made f/10 and f/6 MCTs and there are also widefield desings with a Maksutov meniscus (e.g. by Zen) but I do not see the point in using a smallish "Chinese" MCT with a focal reducer over any other kind of design.

A 5" f/12 (assuming that it is really f/12 and not slower) would become, in the best circumstance, a 5" f/8 with a focal around 1000mm, the 6" could work at 1200mm and the 7" at f/9.5.

The same focals could be attained by reducing an f/10 SCT to f/6, which is a stop faster thant f/8 and a stop and half faster than f/10, so the MCTs suffer from a severe handicap



#14 luxo II

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Posted 13 June 2020 - 08:09 PM

Depends what you’re wanting to observe - for lunar and planetary f/12 and longer - with smaller CO - is a lot better than f/10.

For wide-field lower powers I have a fast APO on the side - beats any SCT.

Therein lies the issue of trying to use an SCT to do everything - it’s jack of all trades and master of none.

Personally I don’t see the point in using an FR for visual - easier to use a bigger eyepiece.

Edited by luxo II, 13 June 2020 - 08:20 PM.


#15 Shorty Barlow

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Posted 13 June 2020 - 08:44 PM


Therein lies the issue of trying to use an SCT to do everything - it’s jack of all trades and master of none.

 

I tend to agree, but SCT's seem to be the most versatile of any design. 



#16 kel123

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Posted 28 April 2021 - 08:39 AM

The main point is however that most MCTs will be still painfully slow even with the focal reducer, and that is a reason good enough to opt for a SCT if the purpose is deep sky AP.
Intes made f/10 and f/6 MCTs and there are also widefield desings with a Maksutov meniscus (e.g. by Zen) but I do not see the point in using a smallish "Chinese" MCT with a focal reducer over any other kind of design.
A 5" f/12 (assuming that it is really f/12 and not slower) would become, in the best circumstance, a 5" f/8 with a focal around 1000mm, the 6" could work at 1200mm and the 7" at f/9.5.
The same focals could be attained by reducing an f/10 SCT to f/6, which is a stop faster thant f/8 and a stop and half faster than f/10, so the MCTs suffer from a severe handicap


I shall continue to say that the myths and bandwagon effect is still very strong in this industry. I have seen spectacular images with reduced Maks, especially galaxies and planetary nebulae. There is nothing wrong with imaging at F/8 if it is what I want to do, it just requires a longer a exposure to achieve the brightness of a faster one.
After all ,people image with RCs at F/8 and it is considered a fine astrograph. People image small galaxies with SCTs at the native focal length of F/10 without stopping the spinning of the earth. I have even seen images captured by maks at F12. Slow but whose time is it?

You are only handicapped if you choose to be. Maks are just like any other scope which cannot do it all. They are as excellent at imaging small targets as SCT if you expose longer.

Let us reduce our equipment bias and naysaying in this industry.
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#17 photoracer18

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Posted 28 April 2021 - 02:46 PM

Intes and Intes Micro made MCT reducers for their Mak-Cass scopes, provided they have moving primary type focusing like SCTs. There were .6x and .55x models. I have one of the .6x models and a .55x one sold recently on one of the forums. That might lead you to think they are common but they are not. I worked for a dealer when they still sold commercial scopes and I have only seen less than a handful of them. If your MCT is F10-F12 you can likely use an SCT one. I would not use them on anything slower like F14-F20. But hey you can always try and it may work good enough.



#18 maroubra_boy

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Posted 29 April 2021 - 03:09 AM

Ok, a scope that produces a flat field from the start would be a Celestron Edge-HD. As does a Mak (or very close to). So, wouldn't it stand to reason that a focal reducer for an Edge-HD scope also work with a Mak???

However, a standard SCT does not produce a flat field, and theres is a focal reducer/corrector for it... so for this reason the reducer/corrector for a standard SCT would not be a suitable match for a Mak, certainly not for a larger chip camera.

All reducer/field flatteners are designed for a specific scope design & focal ratio, and are not interchangeable. This applies to coma correctors too for Newts where any given corrector is optimized for a specific f/ratio, and using it a whole f-stop or more either side will not produce the same quality of edge performance.

This is why I suggest that a focal reducer designed specifically for a scope that produces a flat field from the start would be the most logical place to start, especially when there is no Mak specific reducer currently in production.

I would also suggest borrowing a mate's Edge-HD reducer to try it on your Mak, or buying one second hand - if it doesn't work out then you are more likely to recover your money than from a new purchase.

Alex.

#19 luxo II

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Posted 29 April 2021 - 04:38 AM

MCT's have been available commercially from f/6... f/23. And there are mak-newtonians around f/4.5-f/6 … and IMHO these were much underrated for imaging. Ottiche Zen make and sell f/5.6 photo-visual MCT sets 190-290mm aperture, and complete f/8.5 MCT's 240/290mm aperture. And to that add the diverse catalog Intes and Intes Micro had - f/6, f/8, f/10, f/12 and f/15 examples 5" - 16" aperture.

In short virtually every configuration suited to imaging or visual has been made as a commercial product at some point, a far more diverse range than SCT.

What’s more the Rumaks are flat-field with no coma and negligible spherochromatism, wheras the SCTs have wrestled with these for years and still not really matched what Intes produced as routine.

The challenge is finding one now, as those who have one are unlikely to sell.

The only commercial Schmidt-newtonian (by Meade) was a flop…

Edited by luxo II, 29 April 2021 - 06:55 AM.

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#20 jgraham

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Posted 29 April 2021 - 08:30 AM

I have seen adapters that convert the rear threads on some Maks to a standard SCT thread, from there you can use a standard SCT focal reducer. The tricky bit is that the Maks that I have all give nicely corrected fields in their native focal lengths, a reducer/flattener make over-correct the field.

 

I have done a lot of imaging with Maks, particularly the Meade Mak 7 (7" f/15) and they work fine. They produce a surprisingly well corrected field and an APS-c camera is large enough to frame most deepsky objects quite nicely. I have never used a focal reducer on my Maks, but I have on my SCTs and I always end up taking them off, preferring to leave them at their native focal lengths.

 

Interesting comment on Schmidt Newtonians. Until I got my Mak Newt, my Schmidt Newtonians were my primary platform for going wide. I own 6 Meades from 4 different production lines and 3 Celestrons and of these only one stands out as a bit rough, the Meade 6" f/5 MTS, and it strikes me as an early version of what became the much improved LXD Schmidt Newtonians which went on to enjoy a very long production line. My biggo SN10 remains my primary platform for imaging galaxies; big, fast, and covers an APS-c reasonably well. The venerable SN8 remains the sweet spot in the LXD SN line; not too big, not too small, faster than the SN6 (f/4 versus f/5), much lighter than the SN10. My Meade 6" f/3.6 Schmidt Newtonian was my widest field scope until it was edged out by my 6" f/4.8 Mak Newt using a full frame camera (I don't think that the Meade will cover a full-frame, but I'll find out :) )

 

Food for thought...


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#21 kel123

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Posted 29 April 2021 - 08:45 AM

That will be one hell of a long sub at F/15. What is the faintest target you have imaged at that f ratio?
Do you mind telling why you prefer SCT at native focal length? Image scale for small targets?

#22 Borodog

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Posted 29 April 2021 - 10:23 PM

The Antares f/6.3 SCT threaded reducer is specifically a reducer only and not a flattener/corrector, and I have seen people who have had excellent results on a mak, however I have not personally tried it. I can get as low as f/8.9 on my C90 as is.
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#23 emh52

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Posted 30 April 2021 - 11:16 PM

Ok, a scope that produces a flat field from the start would be a Celestron Edge-HD. As does a Mak (or very close to). So, wouldn't it stand to reason that a focal reducer for an Edge-HD scope also work with a Mak???

However, a standard SCT does not produce a flat field, and theres is a focal reducer/corrector for it... so for this reason the reducer/corrector for a standard SCT would not be a suitable match for a Mak, certainly not for a larger chip camera.

All reducer/field flatteners are designed for a specific scope design & focal ratio, and are not interchangeable. This applies to coma correctors too for Newts where any given corrector is optimized for a specific f/ratio, and using it a whole f-stop or more either side will not produce the same quality of edge performance.

This is why I suggest that a focal reducer designed specifically for a scope that produces a flat field from the start would be the most logical place to start, especially when there is no Mak specific reducer currently in production.

I would also suggest borrowing a mate's Edge-HD reducer to try it on your Mak, or buying one second hand - if it doesn't work out then you are more likely to recover your money than from a new purchase.

Alex.

There is one exception I know of which is the Questar focal reducer but the problem for most would be it has odd threads specific for the Questar's origins in the 1950s that would make it a little difficult to adapt. That said, as a Q owner the focal reducer does work quite well, I recently used it photograph V1405 Nova posted elsewhere in CN (see Questar forum). 



#24 titanio

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Posted 01 May 2021 - 05:07 AM

Hi.

 

In visual yu can use the denkmeir powerswitch in your telescope and you will reduce it at 0.6 X in the lower position. 

 

I use it in my 240 F12. 5 Maksutov and I used it also in my 180 F15:Maksutov. 

 

You must used thouse eyepiece that do not vignetting, like tv plosses or baader zoom, and others.  In case of those eyepieces that vignetting use them a 1.25 baader glasspath, it will increase not much, but you will have less focal.  For instance my old meade 40mm plöss eyepiece vignetting a little bit in the lower position, so I use Baader 1.25 glass Path, and it works pretty good without  vigneting. 

 

You can try also in AP but I have never used it. 

 

Cheers

 

Toni


Edited by titanio, 01 May 2021 - 05:24 AM.


#25 alphatripleplus

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Posted 01 May 2021 - 07:02 AM

I also have the ScopeStuff SCT adapter, which I can attach to the back of my 102mm Mak and use it with a f/6.3 reducer. It works, but as I also have a C6, I tend to just use the Mak without the reducer for visual.




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