Design or Optics quality?

[ollypenrice]

Just now, TareqPhoto said:

What THING?

The scope! The actual real world scope, not its specification on paper. Sorry I wasn't clear.

Olly

[TareqPhoto]

4 minutes ago, ollypenrice said:

The scope! The actual real world scope, not its specification on paper. Sorry I wasn't clear.

Olly

Ok, what do you say or think about this one?

https://agenaastro.com/askar-72mm-f-5-6-quintuplet-petzval-flat-field-astrograph-fra400.html

[ollypenrice]

11 minutes ago, TareqPhoto said:

Ok, let's ignore that FC-60 then, although i heard that this issue is only if using the flattener that is not that good, while using their reducer will fix this issue, but let's not go deep to analyze this scope and compare it with others, i thought a fluorite will always make nice color corrected over any optics for refractor, as i did read an article which shows that fluorite will outperform all optics used in lenses or refractor and they make FPL-53 to be close to it, they even call FPL-53 or FCD-100 as "Synthetic Fluorite", but i think today i learn something new about it.

Well, don't exclude reducers, there are many people using reducers also with amazing results, so i didn't ask to have like 300mm as only native focal length, it can be from reducing the scope also, like from 360mm or 340mm to 270mm-300mm if possible, but sounds you didn't care much about reducers so you try to find super wide aperture to give ~300mm without reducer.

I used the native FS60 to get huge blue bloated stars.

Reducers, no I think that's a good solution provided they work. Generic ones cannot be relied on to work in all scopes, though, even ones within the specified range. I would want to see evidence that a particular combination would work before buying.  Also it is important to be realistic about super-fast effective F ratios. I'd be wary of anything below F4.

Fluorite is fine, too. I have an old fluorite FSQ106 in which the F stands for fluorite, not flatfield, but the best imaging refractor I've ever used is an ED triplet, the Tec 140. It is significantly better than the FSQ106 though it's a slower F ratio, to be fair.

Olly

[TareqPhoto]

10 minutes ago, michael.h.f.wilkinson said:

Reducers can be fine, I get good results on an APS-C sensor with my APM 80 mm F/6 triplet (FPL-53), with a Tele-Vue TRF2008 0.8x reducer, yielding a very useful 384 mm focal length at F/4.8. 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

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.

[david_taurus83]

I used the Altair 102 EDR which is their version of the TS FPL53 doublet. I never seen any of the blue bloat that vlaiv is referring to. Twas a very nice scope and it prompted me to buy their 80EDR doublet as a general purpose imaging scope when I got back into mono. The images below were taken with the 102EDR and my Canon 6D.

 

[TareqPhoto]

2 minutes ago, ollypenrice said:

I used the native FS60 to get huge blue bloated stars.

Reducers, no I think that's a good solution provided they work. Generic ones cannot be relied on to work in all scopes, though, even ones within the specified range. I would want to see evidence that a particular combination would work before buying.  Also it is important to be realistic about super-fast effective F ratios. I'd be wary of anything below F4.

Fluorite is fine, too. I have an old fluorite FSQ106 in which the F stands for fluorite, not flatfield, but the best imaging refractor I've ever used is an ED triplet, the Tec 140. It is significantly better than the FSQ106 though it's a slower F ratio, to be fair.

Olly

Takahahsi FSQ105 and TEC140/150/160/180 and add AstroPhysics 130 for example are all high end very expensive scopes, i barely ordered a triplet last year and still waiting which is almost affordable for me, don't want to buy a second one more expensive than that, and i rushed ordering it before i test my ST80 guide scope with 0.8x reducer, so now all what i want to buy is workable nice scope for 280-320mm focal length with or without reducer.

[TareqPhoto]

2 minutes ago, david_taurus83 said:

I used the Altair 102 EDR which is their version of the TS FPL53 doublet. I never seen any of the blue bloat that vlaiv is referring to. Twas a very nice scope and it prompted me to buy their 80EDR doublet as a general purpose imaging scope when I got back into mono. The images below were taken with the 102EDR and my Canon 6D.

 

What are you trying to tell me?!!!

[david_taurus83]

1 minute ago, TareqPhoto said:

What are you trying to tell me?!!!

That a good FPL53 doublet shouldn't produce blue bloating on stars like the image @vlaiv  has posted.

[TareqPhoto]

What do you think about this scope with their own 0.8x reducer?

https://www.astronomics.com/astro-tech-at60ed-60mm-f-6-fpl-53-ed-doublet.html

There is one very similar or almost the same from TS-Optics as well.

[TareqPhoto]

Just now, david_taurus83 said:

That a good FPL53 doublet shouldn't produce blue bloating on stars like the image @vlaiv  has posted.

Ok, what do you think about a doublet with reducer to give me about 280mm-320mm and using a mono camera with only Ha filter or only Lum filter?

And what about a triplet with FPL-53 and massive reducer and APS-C color camera?

[vlaiv]

9 minutes ago, david_taurus83 said:

That a good FPL53 doublet shouldn't produce blue bloating on stars like the image @vlaiv  has posted.

Indeed - I was surprised as well to see that level of CA as well.

I do know that some images taken with ED80 also show slight CA halo and it is also FPL-53 and smaller objective lens and slower than 102 F/7 scope.

I do wonder if filters have something to do with that? I know that proper filters can remove CA blur even with not so well corrected scopes - that is why there are Astronomik L2 and L3 filters.

[TareqPhoto]

2 minutes ago, vlaiv said:

Indeed - I was surprised as well to see that level of CA as well.

I do know that some images taken with ED80 also show slight CA halo and it is also FPL-53 and smaller objective lens and slower than 102 F/7 scope.

I do wonder if filters have something to do with that? I know that proper filters can remove CA blur even with not so well corrected scopes - that is why there are Astronomik L2 and L3 filters.

What about a bad ED doublet used with only Ha filter or only L filter? no color filters or color camera.

[vlaiv]

Just now, TareqPhoto said:

What about a bad ED doublet used with only Ha filter or only L filter? no color filters or color camera.

Even singlet lens can be great with Ha filter. Ha is single wavelength of light and it will be in focus by itself - regardless of the lens type as far as lens optically decent (not much spherical aberration or similar).

L filter is the worst as it covers whole spectrum from 400 to 700nm. It will include all wavelengths and it will show any defocus in wavelengths as either increase in FWHM or even halo around bright stars.

[TareqPhoto]

How much bad blue halo is bad to reject it or not accept it?

Is this any good result for example?

https://www.astrobin.com/full/m9vm6w/0/

[TareqPhoto]

1 minute ago, vlaiv said:

Even singlet lens can be great with Ha filter. Ha is single wavelength of light and it will be in focus by itself - regardless of the lens type as far as lens optically decent (not much spherical aberration or similar).

L filter is the worst as it covers whole spectrum from 400 to 700nm. It will include all wavelengths and it will show any defocus in wavelengths as either increase in FWHM or even halo around bright stars.

Halo with L filter? i thought it will show a mono result no matter if there is a halo or not, and also you mentioned Astronomik L2 and L3 which i know about long time ago, or even consider LP filter that is more suppression than L.

[david_taurus83]

13 minutes ago, TareqPhoto said:

Ok, what do you think about a doublet with reducer to give me about 280mm-320mm and using a mono camera with only Ha filter or only Lum filter?

And what about a triplet with FPL-53 and massive reducer and APS-C color camera?

If shooting mono then a doublet should be fine as your shooting individual channels so you have control from the outset with focusing for each filter and in post processing with regards to control of star sizes. Obviously, if it your having doubts, go for a triplet as they will have better corrected optics.

[david_taurus83]

11 minutes ago, vlaiv said:

Indeed - I was surprised as well to see that level of CA as well.

I do know that some images taken with ED80 also show slight CA halo and it is also FPL-53 and smaller objective lens and slower than 102 F/7 scope.

I do wonder if filters have something to do with that? I know that proper filters can remove CA blur even with not so well corrected scopes - that is why there are Astronomik L2 and L3 filters.

I've always used an IDAS D2 LP filter so it prob adds a decent IR/UV cut into the equation. Havent tried the DSLR on the 80EDR yet either.

[TareqPhoto]

1 minute ago, david_taurus83 said:

If shooting mono then a doublet should be fine as your shooting individual channels so you have control from the outset with focusing for each filter and in post processing with regards to control of star sizes. Obviously, if it your having doubts, go for a triplet as they will have better corrected optics.

I went with one triplet already, but it has FPL-55, i still didn't get it because it is a new model they are making and will be due in March-May as the site mentioned, so it is a triplet, but i am planning to use it with 0.65x reducer and APS-C color camera.

At the same time for my dual imaging, i want another scope next to it to give very similar FOv or better to say 280mm-300mm with my mono 4/3" sensor cameras, so my concern here only only about a second scope to give me wide field of 280-300mm with 4/3" and using one filter only or two [Ha and Lum only], not thinking about involving colors with it even if it is a triplet also, but sounds i couldn't find triplets at 280-300mm, maybe only new scopes that are petzval or quintuplet designs and new in markets.

[vlaiv]

3 minutes ago, TareqPhoto said:

Halo with L filter? i thought it will show a mono result no matter if there is a halo or not, and also you mentioned Astronomik L2 and L3 which i know about long time ago, or even consider LP filter that is more suppression than L.

Yes, guess what this is:

Here is the answer:

[TareqPhoto]

1 minute ago, david_taurus83 said:

I've always used an IDAS D2 LP filter so it prob adds a decent IR/UV cut into the equation. Havent tried the DSLR on the 80EDR yet either.

I have that IDAS D2 for color camera although i don't have a cooled color camera yet.

[TareqPhoto]

1 minute ago, vlaiv said:

Yes, guess what this is:

Here is the answer:

From where the colors come from? I mean or i said use Lum with doublet and colors with triplet, the halo is blue, so from where that blue came from if Lum is all colors anyway?

[vlaiv]

3 minutes ago, david_taurus83 said:

I've always used an IDAS D2 LP filter so it prob adds a decent IR/UV cut into the equation. Havent tried the DSLR on the 80EDR yet either.

It does eat into violet part of spectrum a bit - so might be part of explanation

[TareqPhoto]

I mean L is full spectrum + UV/IR cut, so colors are coming from RGB or color camera, not L with mono.

[TareqPhoto]

Just now, vlaiv said:

It does eat into violet part of spectrum a bit - so might be part of explanation

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

[vlaiv]

1 minute ago, TareqPhoto said:

From where the colors come from? I mean or i said use Lum with doublet and colors with triplet, the halo is blue, so from where that blue came from if Lum is all colors anyway?

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).