A thinnest high-quality manual or electronic rotator (CAA)

[Vroobel]

Hi.

I know that the CAA is not a camera, but it's closest to the discussion subject. Sorry, if someone asked the question earlier, but I didn't find the answer if any exists here.

My question is what is a thinnest manual (but high-quality one) or electronic rotator. I found one 16 or 16.5 mm thick, while others are only thicker. I'm a user of an Askar FMA230 which has a back focus 52-53mm instead of the declared 55mm and I'm not the only one. I like it and I don't want to swap it with another small scope, but using an ASI 2600MM-Pro cam and a 7 x 2" EFW with its 2mm thick M54/M48 reducer I'm limited now to 13mm only. 

I'm very curious if I missed something in the market. 

Thanks for your help in advance. 

[vlaiv]

I don't know if this qualifies as high quality one - but it is just 5.5mm thick:

https://www.teleskop-express.de/shop/product_info.php/info/p5547_TS-Optics-T2-Thread-360--Rotation-and-Quick-Changer---5-5mm-short.html

I have it on my wide field setup - Samyang 85mm T1.5 lens + suitable adapter and ASI178mcc

[Vroobel]

Thank you Vlaiv, it's indeed very thin. I'd like to use it with an APS-C camera and 20+2 mm EFW, isn't the M42 too small for 39.5 mm from the camera sensor? And isn't 1,350 kg a risky amount?

Thanks and CS

[vlaiv]

2 minutes ago, Vroobel said:

Thank you Vlaiv, it's indeed very thin. I'd like to use it with an APS-C camera and 20+2 mm EFW, isn't the M42 too small for 39.5 mm from the camera sensor? And isn't 1,350 kg a risky amount?

Thanks and CS

Maybe place it between camera and filter wheel?

That way you will only have weight of the camera hanging on it and that is probably a bit less.

M42 also won't be a problem as I'm guessing you are already using that to connect EFW with the camera?

Only drawback is that you'll need to redo flats when you change camera orientation (which you should really do anyway just in case telescope is causing uneven illumination and not just filter wheel / dust on filters).

You can always see if there will be any vignetting by using approximation. You say that you are at 40mm away from sensor and you are using M42 - so let's say that you have 38mm of clear aperture (2mm on each side for adapter). APS-C diagonal is ~28mm so we have (38 - 28) / 2 = 5mm of "room" on each side.

In order for light beam to converge 5mm in 40mm of distance - you need to be at F/4 or faster (that is 10mm of aperture over 40mm of distance or 5mm from center down to center). I think you'll be fine at that distance with most scopes unless you have very fast optics - faster than F/4.

[Vroobel]

Just now, vlaiv said:

Maybe place it between camera and filter wheel?

That way you will only have weight of the camera hanging on it and that is probably a bit less.

M42 also won't be a problem as I'm guessing you are already using that to connect EFW with the camera?

I cannot do it, the camera is screwed straight to the EFW, so it's the first part after the camera.

I can experiment and screw in an M48/M42 reduction behind the EFW to check the vignetting. I use an Askar FMA230 which is F/4.6.

 

[Vroobel]

I'd like to update this thread in case someone has a similar problem.  

Recently I bought two used M54/M54 manual rotators from @rsarwar. One of them has a male M54 / female M48 reduction ring which is great for me, I had only screwed it in deeper to obtain a proper length. It matches perfectly with the 7x2" ZWO EFW with its M54 thread while the second side can be screwed to the Askar thanks to the reducer.

I still think about the 5.5mm rotator, but I'll try to find a similar one with M48 or M54 thread. The extremely low profile would allow me to make an electronic rotator based on that. Thank you, Vlaiv.

CS,

[Clarkey]

I got one of these. 12.5mm thick. I thought it would be really poor, but it is actually very smooth and does not move at all. Holds my 1600mm and filter wheel no problem.

https://www.aliexpress.com/item/1005003279695931.html?UTABTest=aliabtest481469_657498&src=google&src=google&albch=shopping&acnt=494-037-6276&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=17859472720&albag=&trgt=&crea=en1005003279695931&netw=x&device=t&albpg=&albpd=en1005003279695931&gad_source=1&gclid=Cj0KCQiA2KitBhCIARIsAPPMEhLTLkAfDYp7Ma4wdJBuNQrt_M1k1jcWA7ZBuzXiKQhHQq-cRGfRaIkaAuogEALw_wcB&gclsrc=aw.ds&aff_fcid=a1fef4d7886f4bed90c532c4f34b6941-1705697101389-07968-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=a1fef4d7886f4bed90c532c4f34b6941-1705697101389-07968-UneMJZVf&terminal_id=4a377cf5f14743aba676a791ef9a56a1&OLP=1086700608_f_group3&o_s_id=1086700608&afSmartRedirect=y

[Adam J]

On 13/01/2024 at 23:02, Vroobel said:

I cannot do it, the camera is screwed straight to the EFW, so it's the first part after the camera.

I can experiment and screw in an M48/M42 reduction behind the EFW to check the vignetting. I use an Askar FMA230 which is F/4.6.

 

Why not just rotate the whole scope in its rings? Seems no disadvantage to doing that with the FMA230, it has no focuser to orientate for example and the guide scope wont be attached to the tube, its on the rings. 

Adam

Edited January 20 by Adam J

[Vroobel]

It's difficult to rotate the whole scope while a Deep Sky Dad's EAF adapter is used. Rotation by 90* means turning a focusing ring also by 90* in an opposite direction that causes significant change of the focus point. This affects a whole filters offset settings. The FMA230 isn't a typical refractor. 

[Vroobel]

On 19/01/2024 at 20:49, Clarkey said:

I got one of these. 12.5mm thick. I thought it would be really poor, but it is actually very smooth and does not move at all. Holds my 1600mm and filter wheel no problem.

https://www.aliexpress.com/item/1005003279695931.html?UTABTest=aliabtest481469_657498&src=google&src=google&albch=shopping&acnt=494-037-6276&slnk=&plac=&mtctp=&albbt=Google_7_shopping&albagn=888888&isSmbAutoCall=false&needSmbHouyi=false&albcp=17859472720&albag=&trgt=&crea=en1005003279695931&netw=x&device=t&albpg=&albpd=en1005003279695931&gad_source=1&gclid=Cj0KCQiA2KitBhCIARIsAPPMEhLTLkAfDYp7Ma4wdJBuNQrt_M1k1jcWA7ZBuzXiKQhHQq-cRGfRaIkaAuogEALw_wcB&gclsrc=aw.ds&aff_fcid=a1fef4d7886f4bed90c532c4f34b6941-1705697101389-07968-UneMJZVf&aff_fsk=UneMJZVf&aff_platform=aaf&sk=UneMJZVf&aff_trace_key=a1fef4d7886f4bed90c532c4f34b6941-1705697101389-07968-UneMJZVf&terminal_id=4a377cf5f14743aba676a791ef9a56a1&OLP=1086700608_f_group3&o_s_id=1086700608&afSmartRedirect=y

Yeah, it's exactly the same. 

I can see a tiny coma on one edge, depending on the camera position. My 7x2" ZWO EFW with filters and the camera weight more than 1kg, and they pull the camera side of the rotator down, but it's still acceptable. I'll wait a bit, it looks like ZWO plans to introduce their own rotator. 

Edited January 22 by Vroobel

[Adam J]

On 20/01/2024 at 12:41, Vroobel said:

It's difficult to rotate the whole scope while a Deep Sky Dad's EAF adapter is used. Rotation by 90* means turning a focusing ring also by 90* in an opposite direction that causes significant change of the focus point. This affects a whole filters offset settings. The FMA230 isn't a typical refractor. 

Yeah, that's why I made my own focuser adapter and mounted it to the tube itself so that everything rotates as one. You dont need all the complicated sliding stuff he uses as to focus all you need is 5 -10 degrees of total focuser turn, so the longitudinal movement during autofocus is nothing and can be taken up totally by a tiny bit of belt flex. DSD is a over complicated solution. 

Adam

 

 

Edited January 21 by Adam J

[Vroobel]

Thank you Adam, I'm going to consider this idea. 

Edited January 21 by Vroobel

[Vroobel]

On 03/01/2024 at 19:25, vlaiv said:

I don't know if this qualifies as high quality one - but it is just 5.5mm thick:

https://www.teleskop-express.de/shop/product_info.php/info/p5547_TS-Optics-T2-Thread-360--Rotation-and-Quick-Changer---5-5mm-short.html

I have it on my wide field setup - Samyang 85mm T1.5 lens + suitable adapter and ASI178mcc

 

Hi Vlaiv,

I'm pleased to inform you that I ordered the CAA which you linked earlier. The good news is that Altair Astro has it in their offer, so we don't need to pay a fortune for a delivery from Germany.   

https://www.altairastro.com/ts-optics-t2-thread-360-rotation-and-quick-changer---55mm-short-9235-p.asp

I will use it in another project: a Sigma 40mm F/1.4 Art and ASI2600MC Pro with this CAA and a slightly modified female Canon EF/M42 adaptor which I bought from @steppenwolf.   I need the rotation in this setup for mosaic reasons: without the rotation, the mosaic would look like the one below.

 

 

 

[TiffsAndAstro]

11 hours ago, Vroobel said:

 

Hi Vlaiv,

I'm pleased to inform you that I ordered the CAA which you linked earlier. The good news is that Altair Astro has it in their offer, so we don't need to pay a fortune for a delivery from Germany.   

https://www.altairastro.com/ts-optics-t2-thread-360-rotation-and-quick-changer---55mm-short-9235-p.asp

I will use it in another project: a Sigma 40mm F/1.4 Art and ASI2600MC Pro with this CAA and a slightly modified female Canon EF/M42 adaptor which I bought from @steppenwolf.   I need the rotation in this setup for mosaic reasons: without the rotation, the mosaic would look like the one below.

 

 

 

I'm probably misunderstanding but those panels look like they each have a different rotation?

Also interested how you get on with this rotator as it's possibly ideal for me 

Edited September 4 by TiffsAndAstro

[Vroobel]

🙂

Actually, those panels are not rotated, they represent exactly the piece of the sky where the camera is aimed at. The rotator (automatic one, if possible) is needed to counteract distortion of the final image. 

BTW, ZWO declared that they release their electronic automatic rotator (EAR? 🤔) by the end of this year. The wide-field mosaics are the only reason that I think about the EAR. 

 

[vlaiv]

I'm not sure if it is the camera that is rotated or the image beneath the FOVs.

If you take a planetarium software and turn on equatorial grid, align sensor to equatorial grid - say longer edge to RA axis - no matter where you move the FOV - it will still be aligned so that longer edge is along RA.

 

Problem is that in such a wide field of view - RA lines stop being lines - depending on projection. They are always lines on a sphere - but sphere has positive curvature and you can't map it on a plane (like on image) without distortion because image / plane has zero curvature (it is indeed flat surface).

This is why there are different projections when trying to put map of the world on a plane (map a globe to a flat surface).

Now, depending on chosen projection - you will see different level of distortion.

What you are looking for is to image large area of summer MW, right?

Look at this "blink" gif that I made in Stellarium - it uses two different projection methods (stereographic and orthographic) - both used to draw sphere on a flat surface (computer screen) - yet they distort image differently:

One shows RA lines slightly more bent in the corner than the other.

In another words - you don't need rotator - as you will capture adjacent patches of the sky along RA/DEC grid. What you need is to decide on what sort of projection you want to use to make final image and see what software supports that.

[Vroobel]

Usually, it's not a problem to place the rotator (CAA) between the camera and the OTA, but the problem appears if a photographic lens plays a role of the OTA. Thankfully, I am a Canon 6D user, so all my lenses have the EF bayonet and they are short in opposition to lenses for mirrorless cameras with a short flange distance. Recently I bought a ZWO filter drawer including a female EF bayonet to experiment under my Bortle 9+ sky with filters. Unfortunately, I couldn't find the CAA equipped with the same bayonet as easily. There is a 26.5mm space between the lens and the camera. A few months ago I bought a used custom-made 24.5mm long EF/T2 adapter which is 2mm less than typical. It was still too much to consider the ultra-thin 5.5mm CAA placed in the optical train. As a DIY/ATM enthusiast, I have proper tools, a 3D printer and some skills to perform a bigger amendment of both the EF/T2 adapter and the CAA and reach the desired 26.5mm together with durability and safety.

Original thumb screws blocking the rotating part seem small if we take a diameter of the 2600MC camera into account. I didn't take a picture, but it's very difficult to operate with them when the CAA is screwed to the camera. I used 20mm long pieces of 8mm aluminium pipes which have 5mm internal diameter - perfect as an extension of the original screws. I press them into the pipes using a vice. 

 

 

I already had a spare 16.5mm T2 extension so I decided to use it inside a part of the EF adaptor. The 16.5mm extension was too long, so I shortened it to obtain a 10mm length. I could buy the 10mm long extension, but it's another cost and extra time spent on waiting for delivery.

 

 

Using a FreeCAD and 3D printer I obtained a ring which I pressed (with a significant force) between the 10mm T2 extension and the part of the EF adaptor.  I considered an epoxy resin in the beginning but it turned out that it wasn't necessary.

 

 

The 5.5mm CAA contains a rotating part which has a conic profile. Together with an also conic shape of the thumb screw tips it makes that the rotating part is pulled into the stationary part as it is screwed which makes both flanges of the camera and lens parallel. 

 

 

For easier screwing and unscrewing it, I designed a kind of knob. I pressed the knobs on the aluminium extensions of the screws also using the vice. No glue again.

 

 

Usually, I work with two orientations/compositions: horizontal and vertical, so using the following tools I marked positions representing the orientations. I took a text printed on the camera body as a point of reference which is good enough, but it's not obvious in the case of some other cameras.

 

 

The ultra-thin CAA can hold up to 1.5kg which is over twice the weight of the 2600MC. 👍

I think I can use feedback offered by an ASIair informing me about the current angle after each plate solve. Hopefully, I can reach the desired angles after a few attempts.

 

 

Happy users of RedCat or similar scopes who have the CAA with a scale can omit this step. In fact, it's nothing too difficult, so I'm glad that I have a chance to make a better mosaic when the time comes. In the meantime, I'll wait for a ZWO rotator (EAR ?)...  

 

Edited September 10 by Vroobel