Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Sharpstar 61 EDPH II APO Chromatic Abberation?

  • Please log in to reply
169 replies to this topic

#126 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 26 April 2021 - 12:04 PM

Sharpstar's website does not have the pair of spot diags for both without and with the reducer, just the with, for the specific 61EDPHII scope we are discussing. Can't find it on this thread so here it is. It's dated May 15 2020 but I don't recall seeing it before. 

Yes I wish we could find the spot diagram for the scope without reducer , im sure ive seen it in the past .



#127 cedric_d

cedric_d

    Sputnik

  • -----
  • Posts: 28
  • Joined: 07 Apr 2021
  • Loc: France

Posted 27 April 2021 - 01:57 AM

I ended up buying the L3 as I would have always wondered otherwise, but unfortunately it was no better than my existing Baader Lum filter, as I suspected from the Graphs which show almost identical blocking point of 420nm. So its on its way back for refund.

So the only broadband filter that ive found is usable with this scope/ reducer is my Astronomik CLS ccd filter, without that the blue fringing is apparent.

I intend to do some more tests without the reducer to confirm its the reducer and not the scope itself, that won't really help as I bought it with the intention of always using the reducer for the wider FOV. Its fine in Narrowband of course, so even just using it for that its worth the money. just a bit disappointed with the fringing issue for Broadband targets.

CLS  solves it totally, but is also such a strong filter I think it blocks the faint stuff like integrated flux nebula and dark nebulas.

Did you try adusting the focus with no filter at all ? I am waiting for the new moon for a full test, but small focus adjustments clearly have a huge impact on the color frindge on my scope.

 

This test was done with no filter and a Zwo EAF motorized focuser at backfocus 55 mm.

 

focussteps.jpg

Edited by cedric_d, 27 April 2021 - 01:57 AM.

  • RichieNg likes this

#128 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 03:03 AM

Did you try adusting the focus with no filter at all ? I am waiting for the new moon for a full test, but small focus adjustments clearly have a huge impact on the color frindge on my scope.

 

This test was done with no filter and a Zwo EAF motorized focuser at backfocus 55 mm.

 

I focus with a Bahtinov mask, so should be spot on, I dont have a motorised focussed but could try the smallest ten of the knob either side of focus to test. 

However ive now removed the reducer ready to test without it again. I want to have 100% proof its the reducer or the scope itself so I can send results to Sharpstar.



#129 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 05:33 PM

Just did some further tests tonight. First tried without the reducer, blue fringing and Ir bloat greatly reduced not perfect but dramatically better, then tried using my old TSRED279 reducer and was shocked to see it actually improved things further to the point that it’s negligible, and surprisingly the corner stars are almost as round as the dedicated reducer and thats without playing with the spacing. 
im not sure how i feel about these findings, I specifically payed extra for the dedicated reducer assuming that would give the best performance with the scope, but now i find that the generic TS reducer which apcan be used on a huge range of focal lenghts, is performing massively better in colour correction and pretty much equal in producing round stars into the corners of the frame ( at least when usijg the medium sized  zwo533 16mm diagonal sensor ) 

where to go from here, ive owned the scope & dedicated reducer since december. If i start using my TS reducer then I feel ive wasted £200 on the dedicated one. Is it too late to return? Maybe i shoukd send my comparison images direct to sharpstar and ask them if i have a right to return the reducer to the supplier? 
not sure if im hurting my chances by posting on here, it may just Pxxxs them off?

Lee


Edited by leemajors, 27 April 2021 - 06:11 PM.


#130 premk19

premk19

    Viking 1

  • *****
  • Posts: 792
  • Joined: 19 Apr 2015

Posted 27 April 2021 - 05:50 PM

Just did some further tests tonight. First tried without the reducer, blue fringing and Ir bloat greatly reduced not perfect but dramatically better, then tried using my old TSRED279 reducer and was shocked to see it actually improved things further to the point that it’s negligible, and surprisingly the corner stars are almost as round as the dedicated reducer and thats without playing with the spacing.
im not sure how i feel about these findings, I specifically payed extra for the dedicated reducer assuming that would give the best performance with the scope, but now i find that the generic TS reducer which apcan be used on a huge range of focal lenghts, is performing massively better in colour correction and pretty much equal in producing round stars into the corners of the frame ( at least when usijg the medium sized zwo533 16mm diagonal sensor ) also gives a bit more redcution of FL more like 250mm vs 275mm.
where to go from here, ive owned the scope & dedicated reducer since december. If i start using my TS reducer then I feel ive wasted £200 on the dedicated one. Is it too late to return? Maybe i shoukd send my comparison images direct to sharpstar and ask them if i have a right to return the reducer to the supplier?
not sure if im hurting my chances by posting on here, it may just Pxxxs them off?
Lee


The 'dedicated' reducer was made for the original doublet version, so looks like it's over correcting when used with the latest triplet. Definitely take it up with Sharpstar. Maybe they'll offer you a refund.

What back spacing did you use with the TSRED279?

#131 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 06:16 PM

The 'dedicated' reducer was made for the original doublet version, so looks like it's over correcting when used with the latest triplet. Definitely take it up with Sharpstar. Maybe they'll offer you a refund.

What back spacing did you use with the TSRED279?

I didn't buy direct, I bought from the uk importer.

With the TSRED279 its a variable reducer which can be used with scopes ranging in focal length anywhere from 350mm to 800mm.

For 350mm FL scopes it says use 70mm spacing, but as the SS61 is 330mmFL I went slightly more I had it roughly at 71.5mm.

Im just sorting out the comparison images to post



#132 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 06:27 PM

at prime focus f5.5 no reducer, Baader UV/IR filter 60 sec exposure.

Native colour correction not perfect but much better than with dedicated reducer.

Attached Thumbnails

  • Screenshot 2021-04-28 at 00.19.46.jpg

Edited by leemajors, 27 April 2021 - 06:31 PM.


#133 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 06:28 PM

F4.5 using dedicated SS reducer Baader UV/IR filter 60 second exposure.

The dedicated reducer shows strong Blue fringing, like its either magifying the native CA or introducing more itself.

Attached Thumbnails

  • Screenshot 2021-04-28 at 00.19.14.jpg

Edited by leemajors, 27 April 2021 - 06:33 PM.


#134 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 06:30 PM

Aprox F4.5 using TSRED279 variable reducer 71.5mm spacing Baader UV/IR filter, 60 second exposure.

The TS reducer seems to be improving the native colour correction, I suspect it has a good ED element.

Almost no fringing and I would be quite happy if the dedicated reducer performed as good :-( , though im sure the dedicated one gives better shape stars into the corners of larger sensors, but for the 16mm chip of my ZWO533 the TS looks as good in this regard too.

Attached Thumbnails

  • Screenshot 2021-04-28 at 00.19.27.jpg

Edited by leemajors, 27 April 2021 - 06:38 PM.


#135 TareqPhoto

TareqPhoto

    Fly Me to the Moon

  • -----
  • Posts: 7,048
  • Joined: 20 Feb 2017
  • Loc: Ajman - UAE

Posted 27 April 2021 - 07:32 PM

That is clearly why i ask questions, people just keep things like 1+1 = 2, and they don't accept that 2+0 = 2, good that i didn't buy this scope with their own dedicated reducer, i did ask someone to test another flattener or reducer, and you did, and that is what i was talking about, thank you very much for you to share this, and if others also tested this scope with another scopes makers that will be a nice help also.



#136 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 27 April 2021 - 08:21 PM

That is clearly why i ask questions, people just keep things like 1+1 = 2, and they don't accept that 2+0 = 2, good that i didn't buy this scope with their own dedicated reducer, i did ask someone to test another flattener or reducer, and you did, and that is what i was talking about, thank you very much for you to share this, and if others also tested this scope with another scopes makers that will be a nice help also.

Id just say that for colour correction it appears my TS is doing much better, but also have to remember the dedicated sharpstar is designed for full large frame sensors, I haven't got a full frame camera, but I do have a Atik383 which has 22mm diagonal sensor and I can comfirm that the dedicated one gave perfect round stars right across that chip albeit with blue fringing, ive only tried the TS reducer with my smaller ZWO533 as thats a OSC and easier to get accurate comparisions of the colour correction. I doubt that the TS will cover full frame chips as it has much smaller diameter lenses. I wonder if the dedicated one has been optimised to get the roundest stars with the biggest sensors at the expense of the colour correction. Though on the previous doublet version of the scope the reducer didn't seem to give blue fringing, is there is some mismatch her between it being originally designed for the doublet and now being use on a triplet?

The marketing for the Triplet showed improved spot diagrams of corner star shapes using the same reducer, which is odd as you would expect just going from doublet to triplet would only improve colour correction bot star shapes, but we actually seam to be getting the opposite effect, from what ive seen the doublet had superior colour correction but stars wren little + shapes in the corners. now with the triplet we have perfect roundness but poor colour correction. aaarrggghh I Dont know if I will ever really understand this fully.



#137 TareqPhoto

TareqPhoto

    Fly Me to the Moon

  • -----
  • Posts: 7,048
  • Joined: 20 Feb 2017
  • Loc: Ajman - UAE

Posted 27 April 2021 - 09:05 PM

Id just say that for colour correction it appears my TS is doing much better, but also have to remember the dedicated sharpstar is designed for full large frame sensors, I haven't got a full frame camera, but I do have a Atik383 which has 22mm diagonal sensor and I can comfirm that the dedicated one gave perfect round stars right across that chip albeit with blue fringing, ive only tried the TS reducer with my smaller ZWO533 as thats a OSC and easier to get accurate comparisions of the colour correction. I doubt that the TS will cover full frame chips as it has much smaller diameter lenses. I wonder if the dedicated one has been optimised to get the roundest stars with the biggest sensors at the expense of the colour correction. Though on the previous doublet version of the scope the reducer didn't seem to give blue fringing, is there is some mismatch her between it being originally designed for the doublet and now being use on a triplet?

The marketing for the Triplet showed improved spot diagrams of corner star shapes using the same reducer, which is odd as you would expect just going from doublet to triplet would only improve colour correction bot star shapes, but we actually seam to be getting the opposite effect, from what ive seen the doublet had superior colour correction but stars wren little + shapes in the corners. now with the triplet we have perfect roundness but poor colour correction. aaarrggghh I Dont know if I will ever really understand this fully.

Doesn't change or matter much for me as long i keep asking questions, because if that TS reducer for example is better for color correction but it can't cover full frame then simply there are other reducer might have both, this is one thing, another thing is, this Sharpstar scope isn't the only scope in the market anyway, there are another Sharpstar scopes, and another brands that have better flattener and reducer which do great in color correction and can cover full frame, it is all part of research and watching people experiences and such.

 

I've got a scope and i will give it a try, now i keep thinking about another scope that is at wide field one similar to this Sharpstar 61, but with better color correction for the flattener/reducer, and giving wife FOV anyway, don't want to mention names here, but your post is showing me that something there are some combos we don't know about and it turns out to work flawlessly, and sometimes it is only part of fun, maybe that dedicated reducer isn't good with Sharpstar same maker, but it might shine perfectly with another brand scope.



#138 UKalwayscloudy

UKalwayscloudy

    Mariner 2

  • -----
  • Posts: 297
  • Joined: 21 Feb 2019

Posted 28 April 2021 - 08:59 AM

Interesting about the TS reducer - thanks for that. I'm using the Altair Variable 1.0 flattener on it to get the native FL. Good shapes to APS-C.

 

I'm using a Hypercam 26c so am tempted to try the TSRED269 as that sounds good to 30mm diagonal and my sensor is about 27mm. TS web page says it does have an ED element and is a refinement of a Riccardi design. I don't actually have blue bloat but that does look tighter in any case. 


Edited by UKalwayscloudy, 28 April 2021 - 09:16 AM.


#139 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 28 April 2021 - 09:55 AM

Interesting about the TS reducer - thanks for that. I'm using the Altair Variable 1.0 flattener on it to get the native FL. Good shapes to APS-C.

 

I'm using a Hypercam 26c so am tempted to try the TSRED269 as that sounds good to 30mm diagonal and my sensor is about 27mm. TS web page says it does have an ED element and is a refinement of a Riccardi design. I don't actually have blue bloat but that does look tighter in any case. 

Funny thing is when the Original doublet version of this scope came out it was called the TS Photoline60 f5.5. this was a year or 2  before Sharpstar marketed it themselves as the Sharpstar61EDPH and it was available with either a dedicated flattener which looked physically similar to the current dedicated reducer in that it screwed into the focuser, or they would supply the scope with the TSRED279 which I guess explains why it works so well with my mike triplet version too. if you look at this Ade ashford review from 2017 it shows both.

https://astronomynow...o-travel-scope/

As with regards to a flattener, I do have an Altair flattener I could try but that would seam pointless for me as I only the bought the scope to use with the reducer to get the widest field of view.


Edited by leemajors, 28 April 2021 - 09:57 AM.

  • UKalwayscloudy likes this

#140 TareqPhoto

TareqPhoto

    Fly Me to the Moon

  • -----
  • Posts: 7,048
  • Joined: 20 Feb 2017
  • Loc: Ajman - UAE

Posted 28 April 2021 - 03:06 PM

Funny thing is when the Original doublet version of this scope came out it was called the TS Photoline60 f5.5. this was a year or 2  before Sharpstar marketed it themselves as the Sharpstar61EDPH and it was available with either a dedicated flattener which looked physically similar to the current dedicated reducer in that it screwed into the focuser, or they would supply the scope with the TSRED279 which I guess explains why it works so well with my mike triplet version too. if you look at this Ade ashford review from 2017 it shows both.

https://astronomynow...o-travel-scope/

As with regards to a flattener, I do have an Altair flattener I could try but that would seam pointless for me as I only the bought the scope to use with the reducer to get the widest field of view.

Just for the test, for others, not for yourself to use, maybe others would like to have a flattener only, so if you tested with yours and it worked perfectly then maybe people will avoid the dedicated one.



#141 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 28 April 2021 - 05:37 PM

Just for the test, for others, not for yourself to use, maybe others would like to have a flattener only, so if you tested with yours and it worked perfectly then maybe people will avoid the dedicated one.

Ok will see what i can do, though another chap in this thread already tested an Altair flattener, a couple of posts up.

i dont mind though and have another reducer i can try at the same time.

Now the thing I cant decide is how to proceed now with the dedicated one, i sent my comparison with the Tsred279  to Sharpstar asking if they can explain whats going on, or if they are in the process of making an improved one but not had a reply to that, i think they did himt to this the last tike i contacted them in December about it.

But say a new improved one was released tomorrow i doubt they will let us swap it, but then again if the current one isnt fit for purpose, should i be asking them or the supplier for a retun, or is 5 months too long for that?

Thats the issue buying astro gear in the UK as we get so few clear nights to test it all.

the dedicated one works great for narrowband, but my main reason for purchasing a fast triplet and reducer was for wide imaging of broadband targets, things like M31, m45 and the faint IFN stuff in cepheus. Now i find I need to either use my CLS filter to mask the issue, but potentially also block the wavelengths of the faint stuff as that filter blocks most yellow, or alternatively use a 3rd party reducer in which case i have paid £200 extra for the dedicated reducer which will then become a paperweight :-(


Edited by leemajors, 28 April 2021 - 05:45 PM.


#142 UKalwayscloudy

UKalwayscloudy

    Mariner 2

  • -----
  • Posts: 297
  • Joined: 21 Feb 2019

Posted 29 April 2021 - 08:09 AM

Leemajors - great bit of detective work there!! Well found on that story. I have ordered the tsred279 now. I’m curious now. I have some other Riccardi gear and it is excellent.

#143 crtastro

crtastro

    Lift Off

  • -----
  • Posts: 11
  • Joined: 10 Aug 2020
  • Loc: Australia

Posted 29 April 2021 - 01:21 PM

Following this thread with interest as I just bought the Sharpstar with the dedicated reducer.

 

Quick question, is the BF measured from the edge of the reducer body (ie camera side) or where the actual glass is (ie focuser side)

 

Cheers



#144 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 29 April 2021 - 01:27 PM

Following this thread with interest as I just bought the Sharpstar with the dedicated reducer.

 

Quick question, is the BF measured from the edge of the reducer body (ie camera side) or where the actual glass is (ie focuser side)

 

Cheers

Its measured from reducer body flange , camera side.


  • crtastro likes this

#145 Stephanh

Stephanh

    Viking 1

  • -----
  • Posts: 806
  • Joined: 14 May 2016

Posted 29 April 2021 - 04:19 PM

 ive only tried the TS reducer with my smaller ZWO533 as thats a OSC and easier to get accurate comparisions of the colour correction. I doubt that the TS will cover full frame chips as it has much smaller diameter lenses. 

Great test you did!   Thank you for this!!It is very useful information!

 

Do you happen to have a DSLR or APS-C OSC to test the shape of stars in corners?

 

Thank you!



#146 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 29 April 2021 - 05:45 PM

Great test you did!   Thank you for this!!It is very useful information!

 

Do you happen to have a DSLR or APS-C OSC to test the shape of stars in corners?

 

Thank you!

I have my atik383 which has a m4/3rds size, then also  have my old moddified canon 1000D which is APS-C size..

Just getting the time to test everything with UK weather isnt easy, if it’s completely clear then im imaging, only do test shots when its a partly cloudy nights.


Edited by leemajors, 29 April 2021 - 05:47 PM.


#147 Stephanh

Stephanh

    Viking 1

  • -----
  • Posts: 806
  • Joined: 14 May 2016

Posted 29 April 2021 - 06:19 PM

I have my atik383 which has a m4/3rds size, then also have my old moddified canon 1000D which is APS-C size..
Just getting the time to test everything with UK weather isnt easy, if it’s completely clear then im imaging, only do test shots when its a partly cloudy nights.

Of course, I understand. Next time it's partly cloudy, trying with the DSLR would be great! Thank you in advance!

#148 crtastro

crtastro

    Lift Off

  • -----
  • Posts: 11
  • Joined: 10 Aug 2020
  • Loc: Australia

Posted 29 April 2021 - 08:46 PM

Its measured from reducer body flange , camera side.

Cheers for the confirmation. It's just weird that there's no glass on that end like the ED80 FF/FR but on the other side.



#149 leemajors

leemajors

    Explorer 1

  • -----
  • Posts: 82
  • Joined: 11 Feb 2013

Posted 30 April 2021 - 03:57 AM

Cheers for the confirmation. It's just weird that there's no glass on that end like the ED80 FF/FR but on the other side.

Thats only because the actual back focus is about 95mm but they already take up some of that with the filter vault part which brings it down to a perfect 55mm, you can actually unscrew that if you need extra back focus for oag's and things.  Have you not looked at the setup guide?


Edited by leemajors, 30 April 2021 - 04:26 AM.

  • crtastro likes this

#150 crtastro

crtastro

    Lift Off

  • -----
  • Posts: 11
  • Joined: 10 Aug 2020
  • Loc: Australia

Posted 30 April 2021 - 04:31 AM

Thats only because the actual back focus is about 95mm but they already take up some of that with the filter vault part which brings it down to a perfect 55mm, you can actually unscrew that if you need extra back focus for oag's and things.  Have you not looked at the setup guide?

Yes I have and have followed it to the letter but was still confused as to the lack of glass at that end lolz.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics