FSQ 106 Purple stars

[kirkster501]

15 hours ago, gorann said:

Aha, but Camera Raw is only for DSLR, isn't it?

No, it works for any colour image - image in RGB mode that is.

[Ken82]

35 minutes ago, Adam J said:

The total difference in focus position between all filters on my Esprit 100 is 0.04mm meaning I don't really have to use filter offsets. So that is horrendous. I assume you are using the same filters as used on the FSQ85? 

Yea I used the same filters/camera on my fsq 85. I don’t use the L filter only an IDAS D2 for luminance so haven’t measured the focus point. I’d imaging it would be where green is so between my R and B focus points. 
 

I agree it is horrendous! 

 

[gorann]

27 minutes ago, kirkster501 said:

No, it works for any colour image - image in RGB mode that is.

It probably has to do with my version of PS, which is CS5, so a bit old (but free from subscription). Here Camera Raw does not have any filter functions (it is not in the Filter menu), it only pop up when I translate RAW images from a DSLR to tiff. So I need to hold on to my Esprits since they come without colour fringing, apparently unlike a Japanese brand.

[kirkster501]

4 hours ago, gorann said:

It probably has to do with my version of PS, which is CS5, so a bit old (but free from subscription). Here Camera Raw does not have any filter functions (it is not in the Filter menu), it only pop up when I translate RAW images from a DSLR to tiff. So I need to hold on to my Esprits since they come without colour fringing, apparently unlike a Japanese brand.

In the latest PS you can just click on camera raw from anywhere and fire it up.

[Ken82]

On 04/07/2020 at 16:49, Stub Mandrel said:

More importantly, when you pay the premium on a multi-element apochromatic scope isn't getting rid of these effects exactly what you are paying for?

 

I’ve got to agree stub! The general consensus seems to be these chromatic aberration artefacts can be removed somewhat  with software. 

But then what’s the point in spending 5/6k on a “4 element super apochromatic telescope” ?

Im quite sure this is a bad example that has slipped through the net. Certainty the colour correction on my FSQ 85 seems perfect to me. 
 

I don’t think there is any doubt now that what I am seeing is lateral chromatic aberration and I think my research has been comprehensive and compelling. 
 

In a way it’s good to learn about these photographic aberrations but I wish I had learnt another way ! 😩

 

 

 

[DaveS]

But is the Tak truly apochromatic? It has 4 elements, but that doesn't guarantee apo status, as it has , I think, an ED doublet OG and another doublet in a Petzval configuration. 

[andrew s]

There are some diagrams in this link which might help you judge your FSQ not sure if it is the same model. It claims to be usable from 400nm to 1000nm

http://www.astrosurf.com/ilizaso/Takahashi FSQ-106ED/FSQ.htm

Regards Andrew

Edited July 7, 2020 by andrew s

[Ken82]

3 hours ago, andrew s said:

There are some diagrams in this link which might help you judge your FSQ not sure if it is the same model. It claims to be usable from 400nm to 1000nm

http://www.astrosurf.com/ilizaso/Takahashi FSQ-106ED/FSQ.htm

Regards Andrew

Thanks Andrew,

interestingly I know the author of this excellent work from speaking to him about a TOA 130 some years ago. (Don’t worry the toa has magnificent Colour correction 😀) 
 

I did ask him back in late May what he thought of my images and the star colour. 
 

He did say he thought the “lenses were not well aligned in a rotary sense and that I’d require support from optique interlinten or Tak Japan. 
 

I’ve had a similar response from most other experienced astrophotographers and optics specialists I’ve contacted. Spacing of elements, radius errors and misalignment are other common responses I’ve had. 
 
I think I’ve sent my images to Just about everyone in the optics world 😀 it’s good to acquire knowledge! 

[andrew s]

@Ken82 sorry I just rubbed salt in your wound but it was unintentional. 

Regards  Andrew 

[dweller25]

As the scope is new it may be time to return it ?

Edited July 7, 2020 by dweller25

[Ken82]

2 hours ago, dweller25 said:

As the scope is new it may be time to return it ?

Yea it’s been returned to takahashi Europe for some testing. Initial tests suggested the scope was a good example but to be fair I’m not sure what sort of test they would do first??? 
 

I’m assuming a collimation and field flatness test would be completed ??? But perhaps not a colour correction/chromatic aberration test ? 
 

Now It’s going for a shack Hartmann test which I’m sure will show the different focus points for RGB. 
 

Although the disappointing thing is they will not tell me the results of the test 🤔 maybe they will share the results with @FLO I’m not sure of anything right now. 
 

Maybe I’ll have to ply Steve and Grants drinks at the next SGL Star party to reveal  the results 😂

On a serious note I’m not bothered about the results all I want is a normal uniform star colour in my images which I get with my FSQ 85 and this camera.  

[dweller25]

Good luck 👍

Just curious - but can you see CA visually ?

Edited July 8, 2020 by dweller25

[Ken82]

On 07/07/2020 at 12:29, DaveS said:

But is the Tak truly apochromatic? It has 4 elements, but that doesn't guarantee apo status, as it has , I think, an ED doublet OG and another doublet in a Petzval configuration. 

Is this the elephant in the room 🤔 I hope not and for a scope that has been on the market for some time and proven its pedigree I would say it’s perfectly corrected. Just a look around for images shows excellent star colour and the scope itself is marketed as “this is the telescope most imaging refractors want to be”

Plus the near perfect correction I appear to have with my fsq 85 would suggest this 106 example is poor. 
 

I came across some tests in my research and on this example the focus position between blue and red is almost perfect 👌 

The intrafocal Ronchi test using a 10 lines/mm grating - very straight lines throughout the colors, the red lines being a little tighter together. Red has just a trace longer focus (at 656nm about 0,01mm longer than at 532nm)

maybe I can even do a ronchi test myself.  Or even a zygo test ? Not sure what that is really, anyone know ? 

One of the responders on cloudy nights posted a cropped image showing the small star colour. Again beautiful uniform star colour with no purple 👌

That's not normal at all. I also have an FSQ106ED and the stars are perfect.

19 hours ago, dweller25 said:

Good luck 👍

Just curious - but can you see CA visually ?

I’ve not used it visually but perhaps a straight through test with a well corrected eyepiece like a televue would be a good test. 

[DaveS]

You could probably do a Ronchi test if you can put a fine grid in an eyepiece, but a Zygo test needs a serious interferometer.

Zygo Testing

[Ken82]

On 07/07/2020 at 12:29, DaveS said:

But is the Tak truly apochromatic? It has 4 elements, but that doesn't guarantee apo status, as it has , I think, an ED doublet OG and another doublet in a Petzval configuration. 

I’ve had a look online and found a fsq 106ED - fsq 106N comparison and description. 

So Judging by this image I’m guessing takahashi wouldn’t publish this if it wasn’t an exceptional apochromatic? 
 

maybe someone can explain the images ?? Im assuming the focus points for RGB are closer than 0.5mm?!

Takahashi company, top-of-the-range manufacturer, has although decided to use ED glasses as well. Stopping the use of Fluorite, mainly for environmental reasons, didn't mean that optical performances have declined. The most obvious example is the FSQ-106ED, that can be judged by the curves of chromatic correction. The result is outstanding : the new ED formula does even better than its Fluorite ancestor ! Moreover, the correction was widened apart from the visible spectrum to adapt to the new demand of the numerical imaging.

[DaveS]

Looking at those graphs I would expect it to be sensibly free of colour, though am still to be convinced that it fulfils the Abbe condition for apochromaticity, which needs three different glass types.

[Ken82]

Ok I better update the thread.

I decided to send the scope back for a refund. Yes the chromatic aberration issue was disappointing but also the focuser was slipping with only a 2kg camera!

I have been able to test the RGB focal lengths of many FSQ's over the summer and im afraid to say there is a big difference from scope to scope. Inevitably the fsq 106 is a doublet design at heart (glass from canon) so it shouldn't really be a surprise. The rear elements play no part in colour correction.

The scopes ive tested vary from exceptional to poor, but of course that is my opinion. The variation ive tested in terms of RGB focal lengths have a difference between 0.07mm and as far apart as 0.54mm.

Personally Id at least expect a FSQ scope to perform to the maximum focal shift range which takahashi advertise as being 0.22mm (check my image)

This has been a very disappointing experience as opposed to buying my fsq 85 some years ago which to me demonstrates takahashi do get it right with these scopes.   For me the exceptionally expensive fsq 106 i bought wasn't even in the same league as my fsq 85 and I just couldn't accept that! Would you?

Ken

[Adam J]

3 minutes ago, Ken82 said:

 

The scopes ive tested vary from exceptional to poor, but of course that is my opinion. The variation ive tested in terms of RGB focal lengths have a difference between 0.07mm and as far apart as 0.54mm.

 

Would love to see a table of results for the scopes you tested.