scope between fl 2032 and 600

[iwols]

well i have the ts optics refractor q100 at fl600mm and a c8 edge at fl2032 and really struggle with the edge so just wondered if there is a refractor near to the edges focal length that anyone could suggest,thanks

[vlaiv]

2000mm FL refractor is going to be that long - so 2 meter long scope.

Why do you need such a large scope and how do you plan on mounting it?

If you are struggling with Edge - why do you think that 2m refractor is going to be easier to handle / use?

In any case - here is frac that is similar in specs to edge:

https://www.apm-telescopes.net/en/apm-lzos-telescope-apo-refractor-2282050-cnc-lw-ii

Price - real bargain at 41K euro

If you just want focal length how about using 5-6" apo with barlow lens?

Why do you want two meter of focal length?

[iwols]

omg vlaiv your right,,would a 2x/2.5 barlow on my 600mm with an atik 414ex ccd work?  would i still be able to use my filter wheel /rotator back focus dependant and where would the barlow go on my imaging train

[vlaiv]

11 minutes ago, iwols said:

omg vlaiv your right,,would a 2x/2.5 barlow on my 600mm with an atik 414ex ccd work?  would i still be able to use my filter wheel /rotator back focus dependant and where would the barlow go on my imaging train

I'd say that x2 telecentric lens will work better in that regard.

Barlows push focus point away from its normal position and magnification they provide also depends on their distance to sensor. Telecentric lens are better -  they have same amplification for quite a range of distances and I think they minimally impact focus position (but that is something to be checked).

Not sure how it will work with your 100mm F/5.8 as it is quadruplet / Petzval like and it needs sensor at exact position. Never tried that combination so I can't tell if it will work properly.

By the way, I think that 100mm F/5.8 is very well matched with Atik 414ex and it's 6.45µm pixel size. Adding telecentric lens will certainly make it over sample at 1.15"/px. You also need increased aperture to utilize certain resolution and after some point - seeing simply dominates and even large scopes can't resolve.

Why are you exactly struggling with EdgeHD? Is it just the size of the scope or something else (tilt, spacing, poor looking stars)?

 

 

[iwols]

poor looking stars really or it may be that im not used to the star size being bigger than my ts optics,collimated back focus ok theres just something,can you suggest a specific lens? to look at

Edited November 12, 2021 by iwols

[vlaiv]

2 minutes ago, iwols said:

poor looking stars really or it may be that im not used to the star size being bigger than my ts optics

Ok, see - that is the thing,

If you add telecentric lens to your TS scope - you won't have "more zoom" - without stars also being larger.

Size of stars in the image has to do with sampling rate and how well it is matched to detail present in the image. Detail in the image will depend on several factors combined - size and quality of aperture, seeing and mount performance.

Once you reach the limit set by detail in the image (and that is measured by star FWHM) any additional "zoom" will simply make your stars look large / bloated.

That limit for most of us, on most days of the year is around 2"/px for scopes up to 4", 1.5-1.6"/px for 6" scopes and 1.4"/px for 8" scopes. On very good night, you can go down to 1-1.2" with 8" scope - but that is rare.

With 100mm F/5.8 and 6.45µm size you have ~2.3"/px - that is very good match - right there close to limit of what looks good. It is no wonder you are happy with star size and that combination.

With 2000mm FL and 6.45µm pixel size, you have 0.67"/px - that is at least twice as much then is realistically needed - it is like zooming in your image x2 - or x2.5 past what looks good. No wonder you feel that stars are large.

10 minutes ago, iwols said:

can you suggest a specific lens? to look at

2" version - https://www.firstlightoptics.com/barlows/explore-scientific-2x-barlow-focal-extender-2.html

1.25" version - https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html

However - I would not try either of those unless someone can confirm that it will work with quadruplet scope. I can't be certain that it will work properly with such scope. It will work fine with regular scope without flattener, but I simply don't know if it will work with your scope at all.

There are some alternatives for you to consider - that might be better choices to get what you want.

1. Replacing your camera?

One of problems that you have is that it is not feasible to bin x2 your camera as it has low pixel count. Binning will produce ~700 x 500 px image - and that is tiny by today's standards.

If you get camera with larger sensor  - maybe it will work better for you?

Say you have camera like atik 16200 with 6µm pixel size and 4500 x 3600 px. You can use such camera in bin x1 mode on TS 100mm for about same resolution you now have - 2.13"/px, and you can bin that camera x2 when you use it on EdgeHD - to make it work at 1.24"/px or even x3 to get 1.86"/px.

Even if you bin x3 - you'll still end up with 1500x1200px image size - that is larger than you have now.

2. Add scope that is about 5-6" and ~900mm of focal length.

It can be refractor - something like this:

https://www.teleskop-express.de/shop/product_info.php/info/p6679_TS-Optics-PHOTOLINE-130-mm-f-7-FPL53-Triplet-APO-Refractor.html

or maybe even 6" F/6 reflector? (not sure if you'll like that, collimation and all)

 

 

[iwols]

tha

3 hours ago, vlaiv said:

Ok, see - that is the thing,

If you add telecentric lens to your TS scope - you won't have "more zoom" - without stars also being larger.

Size of stars in the image has to do with sampling rate and how well it is matched to detail present in the image. Detail in the image will depend on several factors combined - size and quality of aperture, seeing and mount performance.

Once you reach the limit set by detail in the image (and that is measured by star FWHM) any additional "zoom" will simply make your stars look large / bloated.

That limit for most of us, on most days of the year is around 2"/px for scopes up to 4", 1.5-1.6"/px for 6" scopes and 1.4"/px for 8" scopes. On very good night, you can go down to 1-1.2" with 8" scope - but that is rare.

With 100mm F/5.8 and 6.45µm size you have ~2.3"/px - that is very good match - right there close to limit of what looks good. It is no wonder you are happy with star size and that combination.

With 2000mm FL and 6.45µm pixel size, you have 0.67"/px - that is at least twice as much then is realistically needed - it is like zooming in your image x2 - or x2.5 past what looks good. No wonder you feel that stars are large.

2" version - https://www.firstlightoptics.com/barlows/explore-scientific-2x-barlow-focal-extender-2.html

1.25" version - https://www.firstlightoptics.com/barlows/explore-scientific-2x-3x-5x-barlow-focal-extender-125.html

However - I would not try either of those unless someone can confirm that it will work with quadruplet scope. I can't be certain that it will work properly with such scope. It will work fine with regular scope without flattener, but I simply don't know if it will work with your scope at all.

There are some alternatives for you to consider - that might be better choices to get what you want.

1. Replacing your camera?

One of problems that you have is that it is not feasible to bin x2 your camera as it has low pixel count. Binning will produce ~700 x 500 px image - and that is tiny by today's standards.

If you get camera with larger sensor  - maybe it will work better for you?

Say you have camera like atik 16200 with 6µm pixel size and 4500 x 3600 px. You can use such camera in bin x1 mode on TS 100mm for about same resolution you now have - 2.13"/px, and you can bin that camera x2 when you use it on EdgeHD - to make it work at 1.24"/px or even x3 to get 1.86"/px.

Even if you bin x3 - you'll still end up with 1500x1200px image size - that is larger than you have now.

2. Add scope that is about 5-6" and ~900mm of focal length.

It can be refractor - something like this:

https://www.teleskop-express.de/shop/product_info.php/info/p6679_TS-Optics-PHOTOLINE-130-mm-f-7-FPL53-Triplet-APO-Refractor.html

or maybe even 6" F/6 reflector? (not sure if you'll like that, collimation and all)

 

 

thanks vlaiv is there anything cheaper than  the 16200 you could suggest ,looking at the barlows i would not have enough back focus,any thoughts on asi 1600? cheers

[vlaiv]

1 minute ago, iwols said:

tha

thanks vlaiv is there anything cheaper than  the 16200 you could suggest ,looking at the barlows i would not have enough back focus,any thoughts on asi 1600? cheers

Well, sure that you can get cheaper, I just did not how you feel about CMOS sensors and software binning.

I have ASI1600 and like it a lot, but if I was in the market for similar camera today - I'd probably go for ASI294mm instead. It has better QE and it is a bit larger (23.1 mm vs 21.9mm diagonal). Both will work well with 1.25" filters.

ASI294 can be "unlocked" to 2.3µm pixel size.

If you bin that x3 - you'll get 6.9µm pixel size which is very close to what you have now. That will result in 2760 x 1880 px camera.

For use with EdgeHD - you can bin x6 for example - that will give you effective 13.8µm pixel size or 1.43"/px and you will still have 1380 x 940 px - which is similar to pixel count you have now.

I use my ASI1600 on 80 F/6 apo and RC8" scope. With former I use it natively (with reducer / flattener) for 2"/px while with later - I bin either x2 or x3 for 1"/px or 1.5"/px - depending on what I'm imaging.

This is for example 80mm at 2"/px - at 100% zoom (M13):

This is RC8" at 1"/px at 100% zoom (although image is more like 1.5"-2"/px):

 

 

[ollypenrice]

Could you tell us exactly what you want to do with the proposed scope? DS imaging? Planetary and lunar?  I've used focal lengths from 1 metre to 2.6 metres for deep sky imaging of smaller targets and found little difference in the final results.

Olly

[iwols]

Hi Olly ,i used it for planetary and now use it for deep sky just to get a little closer than my 100mm ts 

[iwols]

On 12/11/2021 at 15:48, vlaiv said:

Well, sure that you can get cheaper, I just did not how you feel about CMOS sensors and software binning.

I have ASI1600 and like it a lot, but if I was in the market for similar camera today - I'd probably go for ASI294mm instead. It has better QE and it is a bit larger (23.1 mm vs 21.9mm diagonal). Both will work well with 1.25" filters.

ASI294 can be "unlocked" to 2.3µm pixel size.

If you bin that x3 - you'll get 6.9µm pixel size which is very close to what you have now. That will result in 2760 x 1880 px camera.

For use with EdgeHD - you can bin x6 for example - that will give you effective 13.8µm pixel size or 1.43"/px and you will still have 1380 x 940 px - which is similar to pixel count you have now.

I use my ASI1600 on 80 F/6 apo and RC8" scope. With former I use it natively (with reducer / flattener) for 2"/px while with later - I bin either x2 or x3 for 1"/px or 1.5"/px - depending on what I'm imaging.

This is for example 80mm at 2"/px - at 100% zoom (M13):

This is RC8" at 1"/px at 100% zoom (although image is more like 1.5"-2"/px):

 

 

hi vlaiv what do you think about adding a 0.7 x reducer to my edge to give me that extra fl over my tsoptics@600mm and possibly improve my image with the edge,what would it mean to my sampling rate please

[iwols]

this is an image i took a while back similar to yours but not as clear lum@5 mins