Looking for an OTA recommendation

[chris_g]

I ordered my second mount last week and it should be here Thursday, it a Sky Watcher AZ-EQ5. My 6D with a 300mm focal length zoom lens will ride on it for the time being. So, I need to start looking for a second OTA. I figure I'll reconfigure my ED80 for the EQ-5, it's a little on the heavy side. I'm looking for another OTA with an image circle that will fully illuminate the full frame of the 6D to ride on my EQ-6. I know the Radian Raptor and several of the William Optics scopes will as well at smaller focal lengths that what I have now and those would ride on the EQ-5. So, I'm looking for a longer focal length than what I have now, I wouldn't mind being able to do some planetary with it I'd also want it to be good at visual as well, so it would need to be able to ride on the AZ-EQ5 in AZ mode. I'm thinking at least 1000mm focal length.

Any thoughts and recommendations?

[Lady Fraktor]

A Vixen ED115s is always nice
What is your budget?

[chris_g]

A Vixen ED115s is always nice
What is your budget?

Budget isn't there now, researching so I know how much I need to save for. The mount took everything I had; I was looking at an IOptron GEM28 when the AZ-EQ5 came into stock. I've wanted that one since the beginning for the dual mode.

Question, what optics would I need to see able to see Neptune and Uranus? This scope would eventually be within my means.

https://astrogeartoday.com/explore-scie ... or-review/

[JayTee]

Hi Chris,

I went with this little beauty. It gives me a medium long focal length (1370mm) but with the Astro-Physics CCDT67 focal reducer (FR) it brings it down to less than 1000 FL. Unfortunately for you when I bought it it was only $295. Man, prices have skyrocketed.

https://optcorp.com/products/tpo-6-f-9- ... -telescope

[chris_g]

Hi Chris,

I went with this little beauty. It gives me a medium long focal length (1370mm) but with the Astro-Physics CCDT67 focal reducer (FR) it brings it down to less than 1000 FL. Unfortunately for you when I bought it it was only $295. Man, prices have skyrocketed.

https://optcorp.com/products/tpo-6-f-9- ... -telescope

That is a sweet tube, it will ride on both mounts for imaging, give me the focal length I want but it won't cover the full frame sensor, at least not with either of the reducers it's listed with. Do you know what the image circle is without reducers? And can you see Uranus and Neptune?

Last year this time, the AZ-EQ5 was 1595, now it's 1899. I noticed prices on almost all the gear went up some time in December, uggg! At least it's still well within the realm of possibility.

[JayTee]

Hi Chris,

Instead of asking about the image circle size (unimportant for now) just go to this website to calculate sensor size compatibility with a given OTA. You are asking about a longer FL OTA because you want to image smaller objects. Not only do you need a longer FL but you also need a smaller sensor, and smaller pixels (≤4.0µ). I know this seems counterintuitive but this means that using a smaller sensor on your intended object eg, M101 means it will take up more sq mm on the smaller sensor (plus, it won't come close to extending beyond the edges of the sensor) so it will present itself by taking up more of that sensor when you display the image (it'll be bigger). You can think of it this way, take the diagonal measure of your sensor and use that number as a rough equivalent of an EP of the same size. The smaller the sensor, the smaller the diagonal measure the smaller the notional EP size the larger the object in the FOV. Now, you want to use smaller pixels to get greater resolution, each pixel sees a smaller chunk of sky so you get greater detail.

Go here.
https://astronomy.tools/calculators/ccd_suitability

In case you're dying to know the image circle of this scope, go and input all the data and look at the very bottom square.
http://www.stargazing.net/naa/scopemath.htm

[SkyHiker]

You'll need a scope with a 2.5" focuser and a flat field. Stellarvue sells nice refractors, many with 3" focusers, but pricey. The ED127 comes with a 2.5" one.

Mak-Newts have a very flat field, a good F ratio for AP and can be used for visual as well (with some neck bending and a step stool). The Skywatcher 190 mm Mak Newt looks nice, but it has a 2" focuser and may be heavy (they don't mention the weight). Check Intes too if you are interested, http://www.stellaroptical.com/newt-mn76.htm . I have the MN152, my favorite mid-weight AP scope with 6" aperture. Works great on the AVX. Check Jim Thommes' images, many are taken with it. Again a 2" focuser. For APS/C it is not a problem, maybe flats can correct it for a full frame? One can only hope. It's quite affordable.

For scopes that do not have a flat field, 2.5" field flatteners and coma correctors are not cheap.

There's not much to see about Uranus or Neptune, in a 80 mm you see a blue dot, in a 127 mm a slightly larger blue dot. About 10x smaller than Jupiter. An OTA with an F ratio that is good for AP is usually not good for planets and vice versa.

If you want to image at F/2 consider an 11" Rasa. It's for AP only but imagine how fast! 10 to 15 times faster than an F/7.5 type scope. Alternatively an 11" EdgeHD with hyperstar would be super for both planets (visual too) and imaging at F/2. With these scopes you won't be able to use a filter wheel.

[chris_g]

Hi Chris,

Instead of asking about the image circle size (unimportant for now) just go to this website to calculate sensor size compatibility with a given OTA. You are asking about a longer FL OTA because you want to image smaller objects. Not only do you need a longer FL but you also need a smaller sensor, and smaller pixels (≤4.0µ). I know this seems counterintuitive but this means that using a smaller sensor on your intended object eg, M101 means it will take up more sq mm on the smaller sensor (plus, it won't come close to extending beyond the edges of the sensor) so it will present itself by taking up more of that sensor when you display the image (it'll be bigger). You can think of it this way, take the diagonal measure of your sensor and use that number as a rough equivalent of an EP of the same size. The smaller the sensor, the smaller the diagonal measure the smaller the notional EP size the larger the object in the FOV. Now, you want to use smaller pixels to get greater resolution, each pixel sees a smaller chunk of sky so you get greater detail.

Go here.
https://astronomy.tools/calculators/ccd_suitability

In case you're dying to know the image circle of this scope, go and input all the data and look at the very bottom square.
http://www.stargazing.net/naa/scopemath.htm

As always JayTee, you give good Information and thanks for those sites. I'm asking about image circle because I have a full frame camera and I want to get a scope that will work effectively with that, focal length isn't that important. I've got a 300mm zoom lens that becomes 480mm effective with an APSC sensor. With that I'll be able to see if I want to invest in a Radian Raptor or Willima Optics based on the FOV. Those scopes will illuminate a full frame sensor. Now I want to try and find a scope with a longer focal length that will illuminate the full frame and compare

I'm also asking about longer focal length because I want to be able to see farther out with both my eyes and with a camera. You've given good info about the camera and smaller objects, and I always knew there would be one more camera in my kit, a good quality dedicated monochrome. I just got my filter kit yesterday, a set of Optolong SHO 7mm 2", a UV/IR and L-Pro to replace the APCS clip version and the filter wheel. Now I'm waiting for another adapter so I connect the field flatterer to the filter wheel without extending the image train more than my ED80 can handle, it's going to be close!

[chris_g]

You'll need a scope with a 2.5" focuser and a flat field. Stellarvue sells nice refractors, many with 3" focusers, but pricey. The ED127 comes with a 2.5" one.

Mak-Newts have a very flat field, a good F ratio for AP and can be used for visual as well (with some neck bending and a step stool). The Skywatcher 190 mm Mak Newt looks nice, but it has a 2" focuser and may be heavy (they don't mention the weight). Check Intes too if you are interested, http://www.stellaroptical.com/newt-mn76.htm . I have the MN152, my favorite mid-weight AP scope with 6" aperture. Works great on the AVX. Check Jim Thommes' images, many are taken with it. Again a 2" focuser. For APS/C it is not a problem, maybe flats can correct it for a full frame? One can only hope. It's quite affordable.

For scopes that do not have a flat field, 2.5" field flatteners and coma correctors are not cheap.

There's not much to see about Uranus or Neptune, in a 80 mm you see a blue dot, in a 127 mm a slightly larger blue dot. About 10x smaller than Jupiter. An OTA with an F ratio that is good for AP is usually not good for planets and vice versa.

If you want to image at F/2 consider an 11" Rasa. It's for AP only but imagine how fast! 10 to 15 times faster than an F/7.5 type scope. Alternatively an 11" EdgeHD with hyperstar would be super for both planets (visual too) and imaging at F/2. With these scopes you won't be able to use a filter wheel.

2.5" focus tube, good info. With the Edge HD can you use a filter wheel when the hyperstar isn't installed on it, the camera would mount in the back? The camera moves up front if I understand it correctly and the wheel would block all kinds of light, a filter drawer perhaps? I've been looking at the C9.25 for a while now but from what I've read that it won't illuminate a full frame, but the Edge HD version might. I'll look at the Mak-Newts and 2.5" focus tubes.

Thanks Henk

[SkyHiker]

Search for "Canon D6" on Astrobin. There are several respectable looking images probably taken with 2" focusers. Maybe a good set of flats can handle it. But you have an ED80 with a 2" focuser so try it and see how much of a problem it is. Maybe the reducer causes vignetting problem, in that case check if replacing it with a FF helps. Or maybe it just works.

[chris_g]

Search for "Canon D6" on Astrobin. There are several respectable looking images probably taken with 2" focusers. Maybe a good set of flats can handle it. But you have an ED80 with a 2" focuser so try it and see how much of a problem it is. Maybe the reducer causes vignetting problem, in that case check if replacing it with a FF helps. Or maybe it just works.

Never thought about just a field flattener, good idea. I'm going to run the 6D the next clear night and see how it comes out

Just an FYI, found this on Opt, though it's not in stock at the moment, says it even works out to a full frame sensor...

https://optcorp.com/products/ioptron-2-field-flattener

[chris_g]

@SkyHiker

Found this image taken with the same scope, reducer/flattener and a 6Da, can't find anything on 6Da, assuming it's a modified 6D. He cropped about 100 pixels off all four sides. You can see at the corners of the stars aren't round. Not seeing any vignette though, overall, pretty good image.

https://www.astrobin.com/v0kjr5/0/

[JayTee]

Two quick comments:
I assume you are speaking about the 60Da. This was Canon's entry into the Astro-camera world. They increased the red sensitivity to do a better job of capturing Ha light. It didn't last long on the market.

A full-frame camera used for small objects like planetary nebula and the fainter galaxies is a misdirected effort. Here's an analogy: using a full-frame camera on a small object is like buying 10 acres of land to put a 400 sq' garden on it! There's a huge amount of leftover space that will most likely be cropped out of the image anyway.

[SkyHiker]

Search for "Canon D6" on Astrobin. There are several respectable looking images probably taken with 2" focusers. Maybe a good set of flats can handle it. But you have an ED80 with a 2" focuser so try it and see how much of a problem it is. Maybe the reducer causes vignetting problem, in that case check if replacing it with a FF helps. Or maybe it just works.

Never thought about just a field flattener, good idea. I'm going to run the 6D the next clear night and see how it comes out

Just an FYI, found this on Opt, though it's not in stock at the moment, says it even works out to a full frame sensor...

https://optcorp.com/products/ioptron-2-field-flattener

If you have vignetting, I would stay away from anything that has a long tube. My FF is much shorter, I got it from ES. It's probably this one, https://explorescientificusa.com/produc ... b2ef&_ss=r , I'm not sure but it looks shorter.