New scope to go with ZWO 485MC

[mikemabel]

I am looking to buy a new telescope to compliment my new ZWO 485mc camera

It's to replace my ST 102. I want a wider fov to capture more nebulae if possible . I think a WO Zenith star 72 III may fit the bill ?

Any thoughts please . My budget is up to £600 . My mount is a HEQ5 pro rbm

Thanks

 

 

 

 

 

[Adam J]

5 hours ago, mikemabel said:

I am looking to buy a new telescope to compliment my new ZWO 485mc camera

It's to replace my ST 102. I want a wider fov to capture more nebulae if possible . I think a WO Zenith star 72 III may fit the bill ?

Any thoughts please . My budget is up to £600 . My mount is a HEQ5 pro rbm

Thanks

 

 

 

 

 

With that small sensor and the small ish pixels you would be better off with the 61 as you will get a wider FOV for emission nebula if that is your thing.

If you could push to the GT71 with a reducer then I would say that would be the optimal.

For either of the doublets though I would stick with the flattener, doublets arent really optimal when pushed below F6.

Something like M42 is much more comfortable in the 61 than the 73

Adam

Edited November 26, 2021 by Adam J

[mikemabel]

Thank you Adam J for your feedback

I'll probably keep my ST 102 canon 450 for widefield and use the new scope 485 as my main rig. 

I am tempted by the GT 71 but the essential flattener really bumps up the price of these scopes but then again this hobby is not without its cost. 

I will have a bit of a ponder about this

Again appreciate your feedback

 

[Adam J]

6 hours ago, mikemabel said:

Thank you Adam J for your feedback

I'll probably keep my ST 102 canon 450 for widefield and use the new scope 485 as my main rig. 

I am tempted by the GT 71 but the essential flattener really bumps up the price of these scopes but then again this hobby is not without its cost. 

I will have a bit of a ponder about this

Again appreciate your feedback

 

Essentially a WO61 but from ts and discounted. My suggestion is to snap it up mate. 

[mikemabel]

My only concern is the small 60mm aperture of these scopes. I am not a dedicated image the same target over a few nights guy .

Will this scope give me reasonable data from a 1 to 2 hours session.

 My better half is pushing me to spend more and so I am looking at a GT 81 with the flattener and accept a fov reduction.

What do you think ?

 

 

 

[Adam J]

3 hours ago, mikemabel said:

My only concern is the small 60mm aperture of these scopes. I am not a dedicated image the same target over a few nights guy .

Will this scope give me reasonable data from a 1 to 2 hours session.

 My better half is pushing me to spend more and so I am looking at a GT 81 with the flattener and accept a fov reduction.

What do you think ?

 

 

 

Speed of capture is all about F-ratio once your camera is fixed. I would say that the GT81 is not suited to the camera you have selected as the chip is too small to cover most wide nebula at the focal length of the GT81.

On the other hand you have the GT71 which with its reducer is F4.72 so exactly the same as the GT81 but you will fit a target into the FOV.

Lets look at M42 and M31 and M45 the common beginner targets.

As above you will not really fit M42 and running man into the GT-81 with the ASI485. The non reduced 61 does better, the GT71 will fit it just but I would say the redcat 51 is there for a referance.

M31, only the redcat is going to fit it all in the frame and only the GT71 is wide enough to get M110 into a 2x1 pannel.

You can just about fir the main stats into the Gt81 here but not with much room for error in your framing the GT71 will give you more margin or error and the redcat 51 will get some some of the extended stuff that the others are missing compleatly.

Other Nebula are much larger than any of these targets, such as NGC7000 (north amrica nebula), the heart nebula etc and only the Redcat 51 will allow you to capture the majority of the target in a single panel.

If you have a larger budget sufficient to consider a GT81 ant the required flattener (£1400 total)then I think I would go a different way. I would return the ASI485 if you are still able and I would instead get a ASI533MC Pro cooled camera. The cost of the GT81 - the difference in camera cost will leave you with about 900 pounds for a telescope and flattener. At that point I would go with your original idea of the ZS73 with a 1.0x flattner and you will have a better imaging rig than you would with an uncooled ASI485mc camera and the GT81.

If you do keep the ASI485mc because you have to or want to then I really would take the GT71 over the GT81 with that sensor. You may even have enough left over to get a L-extream filter.

Remember in imaging the speed of capture is goverend by your choice of camera and F-ratio mainly. Not the aperture, aperture only matters if you dont change focal length and hence you have a faster f-ratio.

I would say that none of the scopes you are considering are suitable for smaller galaxies btw, too short a focal length.

Adam

 

Edited November 28, 2021 by Adam J

[Adam J]

double post

 

 

 

Edited November 28, 2021 by Adam J

[mikemabel]

11 hours ago, Adam J said:

Speed of capture is all about F-ratio once your camera is fixed. I would say that the GT81 is not suited to the camera you have selected as the chip is too small to cover most wide nebula at the focal length of the GT81.

On the other hand you have the GT71 which with its reducer is F4.72 so exactly the same as the GT81 but you will fit a target into the FOV.

Lets look at M42 and M31 and M45 the common beginner targets.

As above you will not really fit M42 and running man into the GT-81 with the ASI485. The non reduced 61 does better, the GT71 will fit it just but I would say the redcat 51 is there for a referance.

M31, only the redcat is going to fit it all in the frame and only the GT71 is wide enough to get M110 into a 2x1 pannel.

You can just about fir the main stats into the Gt81 here but not with much room for error in your framing the GT71 will give you more margin or error and the redcat 51 will get some some of the extended stuff that the others are missing compleatly.

Other Nebula are much larger than any of these targets, such as NGC7000 (north amrica nebula), the heart nebula etc and only the Redcat 51 will allow you to capture the majority of the target in a single panel.

If you have a larger budget sufficient to consider a GT81 ant the required flattener (£1400 total)then I think I would go a different way. I would return the ASI485 if you are still able and I would instead get a ASI533MC Pro cooled camera. The cost of the GT81 - the difference in camera cost will leave you with about 900 pounds for a telescope and flattener. At that point I would go with your original idea of the ZS73 with a 1.0x flattner and you will have a better imaging rig than you would with an uncooled ASI485mc camera and the GT81.

If you do keep the ASI485mc because you have to or want to then I really would take the GT71 over the GT81 with that sensor. You may even have enough left over to get a L-extream filter.

Remember in imaging the speed of capture is goverend by your choice of camera and F-ratio mainly. Not the aperture, aperture only matters if you dont change focal length and hence you have a faster f-ratio.

I would say that none of the scopes you are considering are suitable for smaller galaxies btw, too short a focal length.

Adam

 

Thanks for that information Adam . I've decided to keep the 485 and get the GT 71 ..if I can find it in stock. If not then I will go with the S73 and depending on finances look to a 533 in the near future.

Again thank you for taking the time to explain things .

Mike

[Ags]

How about an Askar 135mm f4.5? That would be sustantially wider, faster and lighter. I don't own one and have never user one, but I am considering one for my ASI485MC. 

[vlaiv]

If 135mm focal length is an option - then Samyang 135mm F/2.0?

Stopped down to 2.8 - it will have very good definition over the surface of smaller chip like 485. Only issue is pixel size (with any of these scopes really as it is 2.9µm - too small), but you can use super pixel mode / bin.

[Ags]

The pixel size is really more like 5.8 um from the point of view of resolution because of the bayer matrix, isn't it?

[Adam J]

12 minutes ago, Ags said:

The pixel size is really more like 5.8 um from the point of view of resolution because of the bayer matrix, isn't it?

depends on colour channel. Green is something like 1.333x native scale and blue and red 1.666 from memory, but its possible to work it out. If you are willing to sacrifice SNR for resolution and dither you can also regain almost all resolution by using bayer drizzel. 

But I do think that the GT71 was a great choice for starting out as it can be a keeper gives a reasonable with that sensor and if he went to a larger cooled sensor later it would still be a great match to many on the market. 

Adam

Edited December 16, 2021 by Adam J

[vlaiv]

16 minutes ago, Ags said:

The pixel size is really more like 5.8 um from the point of view of resolution because of the bayer matrix, isn't it?

Yes it is - but only if you use super pixel mode. Most people use default debayer mode which is interpolation, then you retain sampling rate of smaller pixel.

For full resolution one should really use bayer drizzle - like @Adam J mentioned. It only requires dithering and software support.

That is by the way very good point and OSC sensors should be thought of in that way - bayer element instead of pixel.

For example ASI485mc has 5.8µm pixel size and 1/4 of declared QE in red and blue and 1/2 declared QE in green. That is probably best description of "pixel unit".

[rl]

Given your other half is generously encouraging you to spend more is it worth investigating a GT81 or similar and an APSC SLR camera? I appreciate you've just bought the 485 .....It's a sort of "in the middle" camera with a medium area 11mm by 6mm, no cooling and very small pixels. It would do well on the smaller DSOs, better on solar system stuff. But secondhand 1200D cameras come up fairly frequently standard or modded for between #100 and #250. Still no cooling  but they offer a lot more FOV. With the reducer the GT81 works at about f/4.9 which is pretty quick. 

As you specifically  mention doing visual as well, the 80mm scopes do show a lot more than the 60mm ones. 60mm is great for portable but a bit limiting if it's your main visual option at home. 

Which are you more likely to keep hold of in the long run; the scope or the camera?

[Adam J]

On 16/12/2021 at 18:09, rl said:

Given your other half is generously encouraging you to spend more is it worth investigating a GT81 or similar and an APSC SLR camera? I appreciate you've just bought the 485 .....It's a sort of "in the middle" camera with a medium area 11mm by 6mm, no cooling and very small pixels. It would do well on the smaller DSOs, better on solar system stuff. But secondhand 1200D cameras come up fairly frequently standard or modded for between #100 and #250. Still no cooling  but they offer a lot more FOV. With the reducer the GT81 works at about f/4.9 which is pretty quick. 

As you specifically  mention doing visual as well, the 80mm scopes do show a lot more than the 60mm ones. 60mm is great for portable but a bit limiting if it's your main visual option at home. 

Which are you more likely to keep hold of in the long run; the scope or the camera?

I would say that the IMX485 is a more senstive sensor than the one in a 1200D by some margin. From what i have read the peak QE of that sensor is only 40% in the green and read noise is over 2e. With the 485 you are looking at more like 80-90% in the green and 1e readnoise. So long as the target fits on the 485 sensor there is no argument for the 1200D.

Adam

[ollypenrice]

I was about to suggest the Samyang 135 as a possibility as well. It is fast and will open up your FOV while giving astonishingly sharp results.

There's a whole thread on here about this lens.

Olly