Design or Optics quality?

[TareqPhoto]

1 minute ago, vlaiv said:

Luminance is no different than shooting with color camera - all the wavelengths are recorded at the same time.

In case of mono + luminance - they all end up in gray value of the pixel

in case of color camera - they get distributed between pixels with different filter on them.

You would get the same if you used mono + color filters - and shoot without focus change on each filter and then add all channels together. Only advantage that mono + filters has is ability to refocus on each filter (it has other advantages - but in this context only one is that one).

Ok, add refocusing to the questions, i actually have an autofocuser that i will use, and i will buy another for this second scope i am searching, so focusing is a must here, i will use a Bahtinov mask if i don't use any motor, i thought you all are already thought i will do imaging with dead spot on focus with each filter anyway.

But that wasn't my plan, my plan is to use Ha or Lum only from this ultra wide 280-300mm scope and the color from my 90mm triplet reduced scope, that was the plan.

[vlaiv]

4 minutes ago, TareqPhoto said:

Does eat? The problem is that it has a BIG gap between 550nm and 650nm for vapor sodium mainly LP.

Fact that there is gap between 550nm and 650nm is irrelevant for my reply on blue halo with 4" f/7 doublet scope and use of filter.

[TareqPhoto]

Just now, vlaiv said:

Fact that there is gap between 550nm and 650nm is irrelevant for my reply on blue halo with 4" f/7 doublet scope and use of filter.

Thanks for English dictionary.

Well, the gap is about colors in the range, not about the halo, so i don't know what missing colors it will be for that range or how intensity of colors in that reduced wavelengths, not talking about blue or red.

[TareqPhoto]

So, until now i still don't know which small aperture 60mm scope with reducer to get then.

[vlaiv]

1 minute ago, TareqPhoto said:

But that wasn't my plan, my plan is to use Ha or Lum only from this ultra wide 280-300mm scope and the color from my 90mm triplet reduced scope, that was the plan.

With Ha filter - you can pretty much use any decent scope as that is single wavelength of light and as it is single wavelength of light - it will always be in focus with itself - provided that you focus it properly.

With Luminance filter - you have a problem. You are trying to shoot many wavelengths of light at the same time. With doublet scope - only 2 of them will be in focus at the same time, and with triplet scope - only three of them.

Advantage that triplet scope has over doublet is that other wavelengths will be only slightly defocused - not enough to make blur, but with doublet scope, it can happen that some of wavelengths are so out of focus that they create blur or even halo.

Look at this graph:

This is focus position versus wavelength for doublet type scope. At any time you can have two wavelengths at zero position. All other colors of the rainbow (or wavelengths) are slightly out of focus - and further towards red or violet part of spectrum you move - more defocused they become.

This is same graph for triplet:

It also has some wavelengths being out of focus - but out of focus is much smaller for triplet than for doublet and also, because this curve crosses focus line 3 times - most of the wavelengths are only very slightly defocused.

This means that you will have better / sharper image without halos with triplet than with doublet - when shooting Luminance - as lumanace records all those wavelengths at the same time.

 

[vlaiv]

8 minutes ago, TareqPhoto said:

So, until now i still don't know which small aperture 60mm scope with reducer to get then.

Sorry that I was not more helpful with that - if you can find, ideally you want small 60mm triplet, but if you can't find one - look at images taken with OSC cameras and 60mm doublets without filters and choose telescope that gives best/sharpest images without any trace of blue halo around stars.

[TareqPhoto]

2 minutes ago, vlaiv said:

Sorry that I was not more helpful with that - if you can find, ideally you want small 60mm triplet, but if you can't find one - look at images taken with OSC cameras and 60mm doublets without filters and choose telescope that gives best/sharpest images without any trace of blue halo around stars.

I don't know how much of blue halo is acceptable, i saw very nice beautiful images which i think it has some CA or blue halo around some stars, so i am not sure if that is good to be considered or it is too much

[TareqPhoto]

6 minutes ago, vlaiv said:

With Ha filter - you can pretty much use any decent scope as that is single wavelength of light and as it is single wavelength of light - it will always be in focus with itself - provided that you focus it properly.

With Luminance filter - you have a problem. You are trying to shoot many wavelengths of light at the same time. With doublet scope - only 2 of them will be in focus at the same time, and with triplet scope - only three of them.

Advantage that triplet scope has over doublet is that other wavelengths will be only slightly defocused - not enough to make blur, but with doublet scope, it can happen that some of wavelengths are so out of focus that they create blur or even halo.

Look at this graph:

This is focus position versus wavelength for doublet type scope. At any time you can have two wavelengths at zero position. All other colors of the rainbow (or wavelengths) are slightly out of focus - and further towards red or violet part of spectrum you move - more defocused they become.

This is same graph for triplet:

It also has some wavelengths being out of focus - but out of focus is much smaller for triplet than for doublet and also, because this curve crosses focus line 3 times - most of the wavelengths are only very slightly defocused.

This means that you will have better / sharper image without halos with triplet than with doublet - when shooting Luminance - as lumanace records all those wavelengths at the same time.

 

That was my concern, with Ha i think even my achromatic scope can be fine, but it is not that sharp or i didn't like the results so so much as i feel like maybe a triplet will show better Ha result anyway, if that is not the case then i have to neglect Ha from my question completely and focus with LRGB then.

I did read that L will be less sharpness in doublet than a triplet, i started my topic as thinking maybe it is about the optics quality and not only the type of refrctor, so it is likely that a triplet is a must here if LRGB/colors are mentioned, then we should discuss how good is that triplet then.

I posted about a quintuplet scope, from my understanding it is like a triplet with 2 additional optics, so shouldn't this be even better than a triplet or in same level of triplet? i can post a link of ~60mm scope that it is mentioned being a triplet, but it is not FPL-53, so does that means the colors will be fine but the quality of colors are bad due to not using quality or better optics?

Another option is to buy a known triplet and using an aggressive reducer such as 0.65x or 0.6x or even 0.5x, i have 0.5x reducer [not flattener or corrector], can't i place it to the back of a flattener to have 0.5x reducer and flattener at the same time?

[vlaiv]

Just now, TareqPhoto said:

I don't know how much of blue halo is acceptable, i saw very nice beautiful images which i think it has some CA or blue halo around some stars, so i am not sure if that is good to be considered or it is too much

I guess it is up to you to decide.

Mind you, if you are not going to shoot color with this scope, only luminance - then you can judge if image is acceptable for you - by converting it to gray and just looking at it and deciding based on star shapes and overall sharpness.

If you for example find this image to be sufficiently good for your taste:

Then you don't have to worry about slight residual CA at all.

[TareqPhoto]

Is this reducer any good with any scope [refractor] if using only 4/3" sensor camera?

https://www.altairastro.com/lightwave-06x-reducer-289-p.asp

[TareqPhoto]

2 minutes ago, vlaiv said:

I guess it is up to you to decide.

Mind you, if you are not going to shoot color with this scope, only luminance - then you can judge if image is acceptable for you - by converting it to gray and just looking at it and deciding based on star shapes and overall sharpness.

If you for example find this image to be sufficiently good for your taste:

Then you don't have to worry about slight residual CA at all.

Ok, you judge this, what do you think about this image, do you like it? Or you believe it is FULL of blue halos and it is not acceptable by you?

https://www.astrobin.com/c1viz4/?nc=user

[TareqPhoto]

I don't know if Astronomik L3 filter can be a good help here or not, and what about LRGB filters from Astrodon for example, isn't it a high quality brand and filters and they have better design quality and coating?

[vlaiv]

1 minute ago, TareqPhoto said:

I posted about a quintuplet scope, from my understanding it is like a triplet with 2 additional optics, so shouldn't this be even better than a triplet or in same level of triplet? i can post a link of ~60mm scope that it is mentioned being a triplet, but it is not FPL-53, so does that means the colors will be fine but the quality of colors are bad due to not using quality or better optics?

Quintuplet is just triplet with built in field flattener / reducer.

Either get triplet and separate field flattener or if you want all in one package without the need to get the spacing right and all of that - get quintuplet.

Type of glass does not impact quality of colors. If you have triplet scope - it does not matter much if glass used is FPL-51 or FPL-53 or FPL-55 or something totally different - if telescope is good - it will be good regardless of the glass type.

5 minutes ago, TareqPhoto said:

That was my concern, with Ha i think even my achromatic scope can be fine, but it is not that sharp or i didn't like the results so so much as i feel like maybe a triplet will show better Ha result anyway, if that is not the case then i have to neglect Ha from my question completely and focus with LRGB then.

Simple fast achromat will have other issues - astigmatism, spherical and such. How sharp it is will depend on host of factors. There is a good chance that good ed doublet or triplet will be better scope even for Ha than simple achromat - but sometimes simple achromat if optimized can perform equally well on Ha.

If you don't know how to test it or how to optimize it - then it is lottery if you get decent enough fast achromat to be useful for Ha imaging.

7 minutes ago, TareqPhoto said:

Another option is to buy a known triplet and using an aggressive reducer such as 0.65x or 0.6x or even 0.5x, i have 0.5x reducer [not flattener or corrector], can't i place it to the back of a flattener to have 0.5x reducer and flattener at the same time?

Just forget about such aggressive reduction. If you want to image on those focal lengths and that sort of speeds - just look at camera lens instead.

[TareqPhoto]

2 minutes ago, vlaiv said:

Quintuplet is just triplet with built in field flattener / reducer.

Either get triplet and separate field flattener or if you want all in one package without the need to get the spacing right and all of that - get quintuplet.

Type of glass does not impact quality of colors. If you have triplet scope - it does not matter much if glass used is FPL-51 or FPL-53 or FPL-55 or something totally different - if telescope is good - it will be good regardless of the glass type.

Simple fast achromat will have other issues - astigmatism, spherical and such. How sharp it is will depend on host of factors. There is a good chance that good ed doublet or triplet will be better scope even for Ha than simple achromat - but sometimes simple achromat if optimized can perform equally well on Ha.

If you don't know how to test it or how to optimize it - then it is lottery if you get decent enough fast achromat to be useful for Ha imaging.

Just forget about such aggressive reduction. If you want to image on those focal lengths and that sort of speeds - just look at camera lens instead.

Correction, yes for focal length, but i wasn't after speed, i don't care about speed, be it F1 or F4 or F10 i don't care really, but where you will find a scope with say 280-300mm and not fast speed anyway?

Not interested in lenses, i have Canon 300mm prime and the FOV is unbelievable i love, but the results are awful, in fact i liked the result from my achromatic + 0.8x at 320mm more than my Canon 300mm, and if you said i have to stop the lens down as all people said then i really very very much hate the spikes from lenses, i only like spikes from reflectors, believe me, i looked at all possibilities and i feel like i ask so much difficult demand/request, or i just go with any option i see and take the risk.

[vlaiv]

10 minutes ago, TareqPhoto said:

Is this reducer any good with any scope [refractor] if using only 4/3" sensor camera?

https://www.altairastro.com/lightwave-06x-reducer-289-p.asp

You already got answer about that focal reducer back in the thread:

1 hour ago, michael.h.f.wilkinson said:

I have tried a 0.6x reducer, which seems OK on the smaller ASI183MC's sensor, but  even there seems to give slightly eggy stars at the corners, so I haven't dared use it on an APS-C sensor

 

10 minutes ago, TareqPhoto said:

Ok, you judge this, what do you think about this image, do you like it? Or you believe it is FULL of blue halos and it is not acceptable by you?

https://www.astrobin.com/c1viz4/?nc=user

There are couple of things I could object to that image - but it has no CA issues. You need to distinguish between atmospheric / optics scatter or any filter reflections and CA induced halos.

What that scope / lens has is - lateral chromatism - that is not good either.

For example - look at this part of the image:

It looks like blue channel is further away then red - like stars are smeared.

Let's try that technique where we inspect mono image.

What do you think of star quality here?

[TareqPhoto]

2 minutes ago, vlaiv said:

You already got answer about that focal reducer back in the thread:

 

There are couple of things I could object to that image - but it has no CA issues. You need to distinguish between atmospheric / optics scatter or any filter reflections and CA induced halos.

What that scope / lens has is - lateral chromatism - that is not good either.

For example - look at this part of the image:

It looks like blue channel is further away then red - like stars are smeared.

Let's try that technique where we inspect mono image.

What do you think of star quality here?

Your answer is like not an answer to me, it is like you are telling me to give up of what i look for, showing me issues means you want to answer me with no but with examples.

Ok, i will check out more images and see to what degree people are accepting issues, because i think i saw people liked many issues images and i even see winner images having issues, in fact i saw issues with scopes from Takahahsi or TEC or the cheaper Esprit as well, means i have to accept degrees of issues here, otherwise no refractor is good even a triplet then.

[michael.h.f.wilkinson]

1 hour ago, TareqPhoto said:

I was thinking about getting 0.6x reducer, and i will only use it with 4/3" sensor such as ASI1600mm or QHY294M i have, both smaller sensor camera, so you think it is still not good reducer with those?

I mentioned scopes that are having their own reducers, so they are designed for the main scope, although i have 0.8x reducer without its same maker scope but i don't mind buying another scope with its own dedicated reducer, but i think i want wider so there are few in this case.

The ASI183MC has a considerably smaller sensor than the 1600 or 294, so I cannot guarantee anything 

[vlaiv]

3 minutes ago, TareqPhoto said:

Correction, yes for focal length, but i wasn't after speed, i don't care about speed, be it F1 or F4 or F10 i don't care really, but where you will find a scope with say 280-300mm and not fast speed anyway?

If you don't care about speed - then just get 60mm F/6 doublet with focal reducer and if you happen to have any issues with chromatic blur - then stop it down to say 40mm - that will sort out chromatic blur.

Chromatism in telescope is also factor of aperture size - if you stop down aperture you reduce color issues.

5 minutes ago, TareqPhoto said:

Not interested in lenses, i have Canon 300mm prime and the FOV is unbelievable i love, but the results are awful, in fact i liked the result from my achromatic + 0.8x at 320mm more than my Canon 300mm, and if you said i have to stop the lens down as all people said then i really very very much hate the spikes from lenses, i only like spikes from reflectors, believe me, i looked at all possibilities and i feel like i ask so much difficult demand/request, or i just go with any option i see and take the risk

You can stop the lens down in the same way you stop down a telescope - by aperture mask.

If aperture mask is round - you won't get spikes.

If you like your ST80 + reducer that much - why not use it? just stop it down to say 40-50mm and it will reduce CA problems significantly.

This image was taken with ST102 and 66mm aperture mask (I cut aperture mask by hand so it was not perfect circle - that is why there are bunch of tiny spikes on that sharp star - but you can 3d print proper mask or have it cut for you).

[TareqPhoto]

https://www.astrobin.com/wn5x1u/?nc=user

This is a winner image from FSQ106 and Astrodon filters, if i pixel peeping it to full size i can see slightly issues by stars as well, so it wasn't perfect, and maybe the user did huge processing to minimize it also, who knows.

[TareqPhoto]

2 minutes ago, vlaiv said:

If you don't care about speed - then just get 60mm F/6 doublet with focal reducer and if you happen to have any issues with chromatic blur - then stop it down to say 40mm - that will sort out chromatic blur.

Chromatism in telescope is also factor of aperture size - if you stop down aperture you reduce color issues.

You can stop the lens down in the same way you stop down a telescope - by aperture mask.

If aperture mask is round - you won't get spikes.

If you like your ST80 + reducer that much - why not use it? just stop it down to say 40-50mm and it will reduce CA problems significantly.

This image was taken with ST102 and 66mm aperture mask (I cut aperture mask by hand so it was not perfect circle - that is why there are bunch of tiny spikes on that sharp star - but you can 3d print proper mask or have it cut for you).

Your first idea about getting 60mm F/6 and use a reducer and stop it down sounds a great idea, this i can accept and go with, i hope it won't disappoint me later in any cases.

Regarding the lenses, i can do that with my smaller lenses that has filters threads, such as my 70-200 or 135mm or 85mm or even 100-400, but my 300 is huge front and it doesn't have filter thread and i use it with the dew hood that is huge, couldn't find any mask and i have no access to any 3D printer to make some, and i hate the focuser ring of the lens, it is my old lens that needs a lot of service and greasing but i will never send it to service anymore, and the lens itself also have in the back what is called gelatin filter, transparent glass, but it caused FAT ugly halo before when i tested with D2 filter or LRGB filters, so in brief, NO to this lens.

And about my ST80 + 0.8x, i am still using it anyway, i don't have another refractor anyway, and i also using it next to that 300mm lens recently for practice, but i won't use both later at all, ordered a triplet that i still waiting since October, and the second one should be also a scope, can't afford the same triplet again and an expensive reducer for it as second one, so wanted something cheap, now you suggest about 60mm reduced and stopped down that can be a plan, hope that is my answer.

Thank you

[TareqPhoto]

There is also another option i just recently found, this reducer for SCT, can give that FL i want, and razor speed, what do you think about this option then? C6 not sure which version/model reduced with this Hyperstar 6.

https://starizona.com/products/hyperstar-6

[vlaiv]

1 minute ago, TareqPhoto said:

There is also another option i just recently found, this reducer for SCT, can give that FL i want, and razor speed, what do you think about this option then? C6 not sure which version/model reduced with this Hyperstar 6.

https://starizona.com/products/hyperstar-6

It is good if you don't care about star shapes.

There is better option - but not in focal length you want. Celestron has its own model called RASA.

https://www.firstlightoptics.com/optical-tube-assemblies/celestron-rowe-ackermann-astrograph-rasa-8.html

 

[TareqPhoto]

1 minute ago, vlaiv said:

It is good if you don't care about star shapes.

There is better option - but not in focal length you want. Celestron has its own model called RASA.

https://www.firstlightoptics.com/optical-tube-assemblies/celestron-rowe-ackermann-astrograph-rasa-8.html

 

RASA is out of my plan and mind, so not going there.

What star shapes you are talking about?

Ok, this is the last option i left, didn't want to include it as i don't know about this maker reputation much, what do you think, a triplet and there is a reducer for it designed?

https://www.firstlightoptics.com/sharpstar-telescopes/sharpstar-61edph-ii-f5-5-triplet-ed-apo-telescope.html

[vlaiv]

2 minutes ago, TareqPhoto said:

What star shapes you are talking about?

On that page you linked that describes the product - there is example image of M31 taken with that setup.

4 minutes ago, TareqPhoto said:

Ok, this is the last option i left, didn't want to include it as i don't know about this maker reputation much, what do you think, a triplet and there is a reducer for it designed?

https://www.firstlightoptics.com/sharpstar-telescopes/sharpstar-61edph-ii-f5-5-triplet-ed-apo-telescope.html

Don't know much about that scope - but according to this recent discussion:

It might need Astronomik L3 as well.

[TareqPhoto]

2 minutes ago, vlaiv said:

On that page you linked that describes the product - there is example image of M31 taken with that setup.

Don't know much about that scope - but according to this recent discussion:

It might need Astronomik L3 as well.

You see only issues, no hopes.

For the star shapes from that page, i can't judge from that really, the imager used 183 and who knows what conditions and processing he was doing, i will do more research to see if that is the scope issue or the user issues, very easy people to show up issues and relate it to gear more than themselves, but that can happen, i will do more inspect.

About 61, bear in mind that there are two models, the old one 61EDPH original is a doublet, while the version II is a triplet, is that discussion about version 1 or 2 or it doesn't matter?