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Sharpstar 61 EDPH II APO Chromatic Abberation?

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#51 UKalwayscloudy

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Posted 01 December 2020 - 06:16 AM

I've had the triplet Mark 2 from Sharpstar for a while and think the CA is moderate and way better than the Nikon 180mm that this scope has replaced for wide field. So far what fringing I have seen varies depending on what filter I use. 

 

1. Many of the issues can be dealt with by using the defringe tool in Lightroom.

 

2. When doing detailed processing with multi narrowband filters I often get purple fringing even on my more high end scope and also on the Sharpstar. I make the halo removal in Pixinsight as a matter of routine, using the script by Shawn at visible dark.ca. It jukes nukes the purple halos. 

 

https://www.youtube....h?v=EgJfichawXQ

 

3. Sticking in a filter with a stronger cut might help. I got one of those for my Nikon but haven't really needed it with the Sharpstar. Fringe-killer is what they are called. 

 

I am not saying the CA is a non issue or absent but I think there are easy workarounds. 

 

By the way, I am testing a new way of using this scope with a 1.0x flattener. I'm not there yet with the backfocus details and have some tilt, but will share this here. I'm using the Altair Variable 1.0x flattener, and have done some test images with both a Nikon Z6 and Hypercam 269c. My processing includes wiping out the fringes. Here is an example. It's based on a very rough guess for the backfocus so I think I can do better with some tweaks to the spacing on my rig. This is a 4/3 sensor. Full frame images with the Nikon have some distortion in the corners but are fine unless you pixel peep. Astrometry.net came back with a focal length of 340mm, so it's a handy alternative to the FL you get with the standard reducer. 

 

To be honest, I think the CA is a moderate and manageable issue. You get amazing full frame illumination with this scope and with the 0.8 reducer star shapes are great to maybe halfway between  APS-C and full frame. 

 

 

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#52 UKalwayscloudy

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Posted 01 December 2020 - 06:21 AM

This was managed just using Lightroom tools and you can see full res image with the 269c 3.3 micron pixels. I'd only just had the camera for a while and might be able to do it better now. 

 

https://www.astrobin.../full/cwsho9/0/


Edited by UKalwayscloudy, 01 December 2020 - 06:26 AM.


#53 Tommohawk

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Posted 22 January 2021 - 04:34 PM

Hi. FWIW I have the Mk1 version together with the Sharpstar reducer and although the field is nice and flat, it does have CA for sure when used with wider spectrum blue filters. I changed my blue filter for an Astronomik deep sky and this has resolved the issue nicely. 

 

The same is true for the LUM subs - way too soft probably for the same reason. I have just taken delivery of an Astronomik L3 which should sort this hopefully.

 

Here's a link to the Pleiades done with the Astronomik deep sky blue. Because of the LUM issue the LUM was done with an RGB superluminance, so not ideal - it's been stretched a bit too much but no real CA to speak of. 

 

https://stargazerslo...edph-reducer/  

 

Edit Sorry just realised you are using a Canon, not mono. The bayer matrix probably passes a lot of blue. If you can get an L3 filter in system somehow it will help clip the troublesome short wavelength blue. Not sure if thats possible?


Edited by Tommohawk, 22 January 2021 - 04:40 PM.


#54 UKalwayscloudy

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Posted 23 January 2021 - 11:09 AM

Tommohawk - this is very useful to know. Had you tried the Lightroom CA sliders before going to a stronger blue cut?

#55 Tommohawk

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Posted 24 January 2021 - 09:39 AM

Tommohawk - this is very useful to know. Had you tried the Lightroom CA sliders before going to a stronger blue cut?

Cant say I did, I don't usually use Lightroom, but I tried pretty much everything else! Very difficult to process out blue bloating in my experience. If you have purple fringes you can identify and tweak them, if its just blue bloat you cant easily process out - other than by manual selection/cloning etc.  

 

One other point of interest.... when I came to do flats, I expected the exposure time to be longer for the Astronomik Blue compared to my existing blue, due to the reduced bandwidth - but it wasn't. So although cutting the width could remove some detail in the shorter wavelength, it doesnt reduce the overall transmission. FWIW.



#56 TareqPhoto

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Posted 25 January 2021 - 09:08 PM

I was thinking to buy this scope for mono with Ha or Lum only, but with CA i doubt i will get one even for one filter mono, i will look into something else maybe.



#57 spordniar

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Posted 05 February 2021 - 10:04 PM

I wonder if OP had done the proper back-focusing of 55mm from the FF to the sensor, and whether a poor back-focusing distance would be at play introducing the CA.


Edited by spordniar, 05 February 2021 - 10:05 PM.

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#58 Tommohawk

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Posted 06 February 2021 - 03:48 AM

I wonder if OP had done the proper back-focusing of 55mm from the FF to the sensor, and whether a poor back-focusing distance would be at play introducing the CA.



#59 Tommohawk

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Posted 06 February 2021 - 03:51 AM

Yes I wondered the same. Incorrect spacing seems to cause mostly issues with flatness of field but likely causes some CA too

#60 chongo228

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Posted 07 February 2021 - 10:19 PM

Below is a stacked, corrected with darks/flats, and auto stretched image taken with the Sharpstar 61 version 2 with the reducer. You can see I have some tilt that causes CA in the top left and oval stars on the bottom right. The right side doesn't show the blue hue around the stars so maybe improper backspacing is contributing to the OP problem. The CFZ of a F4.1 scope is very small so any improper spacing would make a difference. I suspect mine is caused by my camera (ASI2600mc) that others have reported has tilt from the factory. It might also be from the focuser not handling the weight properly. 

 

The 2600 isn't a full frame chip so maybe it's just not big enough to show the problem.

 

 

Does anyone know if the Radian Raptor or TS61 that are clones of the Sharpstar 61 have the same problem?

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Edited by chongo228, 08 February 2021 - 10:52 AM.


#61 TareqPhoto

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Posted 08 February 2021 - 06:34 PM

Another question is, if they didn't update/improve their reducer since the doublet 61 version, so why can't anyone test another reducer knowing that it is 0.8x anyway? We always trying to trust the same item from the manufacturer to match or be a better compatible with the scope for example, if that wasn't the case then why scared to try something else as a combo?



#62 UKalwayscloudy

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Posted 09 February 2021 - 03:48 PM

Flatteners and reducers usually work best when designed with detailed knowledge of the lens arrangement on the main scope. Generics or devices designed for other scopes are much less likely to work. I did these experiments to find a 1.0 flattener and got lucky on the third time with the Altair variable 1.0 flattener. It worked a lot better than another one designed for scopes around this FR and FL.

#63 TareqPhoto

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Posted 09 February 2021 - 05:51 PM

I was thinking about this scope Sharpstar 61II until people showing issues with reducer, in fact i wanted the scope with the reducer and not with flattener, and that just was enough for me to cancel my decision about this scope.



#64 Tommohawk

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Posted 10 February 2021 - 05:13 AM

Below is a stacked, corrected with darks/flats, and auto stretched image taken with the Sharpstar 61 version 2 with the reducer. You can see I have some tilt that causes CA in the top left and oval stars on the bottom right. The right side doesn't show the blue hue around the stars so maybe improper backspacing is contributing to the OP problem. The CFZ of a F4.1 scope is very small so any improper spacing would make a difference. I suspect mine is caused by my camera (ASI2600mc) that others have reported has tilt from the factory. It might also be from the focuser not handling the weight properly. 

 

The 2600 isn't a full frame chip so maybe it's just not big enough to show the problem.

 

 

Does anyone know if the Radian Raptor or TS61 that are clones of the Sharpstar 61 have the same problem?

That's a useful observation and certainly suggests that spacing may play some part in the CA issue.

 

I cant speak for the triplet version, I have the doublet, but I have to say that in general it's a good scope and mechanically very sound. The focuser is smooth and solid and I don't see any  tilt with my ASI1600 + 7 posn EFW. The flattener/reducer works very well, and stars are a nice shape right across the field. There is slight CA, but this can be resolved by using an L3 type luminance filter. 

 

I any event these (relatively) fast set ups are really sensitive to spacing issues and tilt even with perfect optics.



#65 chongo228

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Posted 10 February 2021 - 06:27 AM

That's a useful observation and certainly suggests that spacing may play some part in the CA issue.

 

I cant speak for the triplet version, I have the doublet, but I have to say that in general it's a good scope and mechanically very sound. The focuser is smooth and solid and I don't see any  tilt with my ASI1600 + 7 posn EFW. The flattener/reducer works very well, and stars are a nice shape right across the field. There is slight CA, but this can be resolved by using an L3 type luminance filter. 

 

I any event these (relatively) fast set ups are really sensitive to spacing issues and tilt even with perfect optics.

I do agree the focuser is solid. I don't think it's the cause of tilt. I believe it is from the camera itself and is a known issue....I mean the camera comes with a tilt plate installed from the factory to correct it. 


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#66 threemcs17

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Posted 12 February 2021 - 09:54 AM

Below is a stacked, corrected with darks/flats, and auto stretched image taken with the Sharpstar 61 version 2 with the reducer. You can see I have some tilt that causes CA in the top left and oval stars on the bottom right. The right side doesn't show the blue hue around the stars so maybe improper backspacing is contributing to the OP problem. The CFZ of a F4.1 scope is very small so any improper spacing would make a difference. I suspect mine is caused by my camera (ASI2600mc) that others have reported has tilt from the factory. It might also be from the focuser not handling the weight properly. 

 

The 2600 isn't a full frame chip so maybe it's just not big enough to show the problem.

 

 

Does anyone know if the Radian Raptor or TS61 that are clones of the Sharpstar 61 have the same problem?

Yes, my Radian Raptor 61 has the same issue and I am ****.  Calling OPT today to see what can be done, but this is freaking unacceptable in a $1,000 "apochromat" "astrograph" triplet -- all words used in "selling" this scope to the masses.  Do they think we are idiots!  I'm so **** right now!  

Rosette Nebula   February 2021
Capture
Orion Purple


#67 TareqPhoto

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Posted 12 February 2021 - 10:16 AM

Yes, my Radian Raptor 61 has the same issue and I am ****.  Calling OPT today to see what can be done, but this is freaking unacceptable in a $1,000 "apochromat" "astrograph" triplet -- all words used in "selling" this scope to the masses.  Do they think we are idiots!  I'm so **** right now!  

And i am not ..... to buy things only based on promotions by manufacturers or by video reviews from popular YouTubers. 



#68 threemcs17

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Posted 13 February 2021 - 10:53 AM

And i am not ..... to buy things only based on promotions by manufacturers or by video reviews from popular YouTubers. 

Well thanks.  You know, Trevor has had a pretty long reputation as a reputable astrophotographer so it was hard not to at least give a look at the scope. I'm a veteran in astrophotography and have used 5+ scopes over the years.  In recent years, I have moved more towards a portable setup that I can take with me all over the world in my traveling.  So, this radian seemed to fit in a nice niche for that purpose.  I didn't just blindly buy on hype.  But I expected more from OPT and Trevor.  Alas, that trust was misplaced.  



#69 TareqPhoto

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Posted 13 February 2021 - 11:49 AM

Well thanks.  You know, Trevor has had a pretty long reputation as a reputable astrophotographer so it was hard not to at least give a look at the scope. I'm a veteran in astrophotography and have used 5+ scopes over the years.  In recent years, I have moved more towards a portable setup that I can take with me all over the world in my traveling.  So, this radian seemed to fit in a nice niche for that purpose.  I didn't just blindly buy on hype.  But I expected more from OPT and Trevor.  Alas, that trust was misplaced.  

My friend, almost ALL videos i watched on YouTube about scopes or cameras they are all positive and great nice reviews, so i can't just believe all of them, and i was watching since 2017 or 2018 and still i don't use those YT videos as my deciding factor, i respect all of them, they do what they do for whatever reasons, i just ask here, i prefer the experience in this forum more than hyped videos honestly, and i bought all my items carefully after long long discussions and search and no regret, i am sure if OPT will produce a new scope again then Trevor will be busy to review it and end up with saying it is highly recommended and it is amazing scope, later on we will see issues, so who to blame here? And i respect Trevor and all others.



#70 UKalwayscloudy

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Posted 14 February 2021 - 07:34 AM

threemcs17 - I think for the price of the Raptor one would expect much better. Many of us realised quickly it was a tarted up SS61EDPH II. But I am still surprised at the level of fringing in your photo. I have nothing like that on my SS61 triplet. Can't help wondering if there is some variation in the glass. Sharpstar don't specify what is in there. I did induce a lot of blue around my stars when I dig some very aggressive processing doing an SHO simulation from H-O data, but that was more to do with me hyping the blue to try and get it up to a decent level in the nebula. Nothing remotely like your image from normal processing, as per link below which us the closest in spirit to the one you have shown. I hope you sort it out - that is really not good enough.  https://www.astrobin...q52wfl/?nc=user



#71 threemcs17

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Posted 15 February 2021 - 08:25 AM

threemcs17 - I think for the price of the Raptor one would expect much better. Many of us realised quickly it was a tarted up SS61EDPH II. But I am still surprised at the level of fringing in your photo. I have nothing like that on my SS61 triplet. Can't help wondering if there is some variation in the glass. Sharpstar don't specify what is in there. I did induce a lot of blue around my stars when I dig some very aggressive processing doing an SHO simulation from H-O data, but that was more to do with me hyping the blue to try and get it up to a decent level in the nebula. Nothing remotely like your image from normal processing, as per link below which us the closest in spirit to the one you have shown. I hope you sort it out - that is really not good enough.  https://www.astrobin...q52wfl/?nc=user

Thanks for the feedback.  Yeah, upon further research and digging, I found that this Radian has a FPL-51 glass and not the industry standard FPL-53. There is something up with this glass and the specific use of CMOS/CCD cameras.  In Trevor's defense, I don't believe he ran in to this in his prototype unit because he just used the Canon EOS RA as his imaging camera. But I'm returning this scope because I don't have the time or enough clear nights to trouble shoot what OPT should have solved before putting this into the market.  The problem is, because of all of the delays with different parts of my order, I'm already beyond my 30-day return window, but I hope they will do the right thing and accept the return.  I'm really disappointed in the performance of this scope.  I'm sure many will assume I did something wrong in my post-processing routine.  However, those photos were just after a few basic levels adjustments and one or two modest curve stretches.  I'm familiar with how stars can get bloated and out of hand rather quickly depending on how you process the image. I can guarantee you that those stars are straight from the scope/camera that way.  I'm going to go with the WO Zenithstar 61 and see how that responds and performs.  



#72 Tommohawk

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Posted 15 February 2021 - 09:21 AM

Yes, my Radian Raptor 61 has the same issue and I am ****.  Calling OPT today to see what can be done, but this is freaking unacceptable in a $1,000 "apochromat" "astrograph" triplet -- all words used in "selling" this scope to the masses.  Do they think we are idiots!  I'm so **** right now!  

The CA in this is pretty bad, it's worse than my Mk 1 version. I can't help but wonder if this is in part due to spacing - some of these fast-ish scopes seem incredibly sensitive to this. Are you 100% confident you have 55mm to the sensor? 



#73 Barologuy

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Posted 15 February 2021 - 12:15 PM

I wonder if OP had done the proper back-focusing of 55mm from the FF to the sensor, and whether a poor back-focusing distance would be at play introducing the CA.



Yeah I have proper backfocus, I have checked it a couple times and it's standardized for me I guess. The combination of the T Ring and the ef-s/ef to ef-m adapter puts the sensor to the threads at the base of the focal reducer right at 55 mm backfocus.

I've since imaged other objects and while I do get CA as other have discussed I just go in and defringe.

#74 UKalwayscloudy

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Posted 15 February 2021 - 12:38 PM

Odd business this. Interesting to see FPL-51 stated for the Raptor. There is that more expensive version that TS-optics sells that is stated to be FPL-53, but it seems us owners of the Sharpstar-branded model (whether doublet or triplet) are not sure what we have. Might even be some variation as SS have not committed themselves. Their web site just says: "Objective type: Triplet air-spaced APO (One element of the lens is made from ultra-low dispersion ED glass)".

 

And then there is this statement on the Agena web site:  

 

"Please Note: In recent days, with the buzz around the Radian Raptor, we have received a few inquiries whether this scope uses FPL-53 glass or whether there are two optical versions of this scope in the market. Based on the information provided to us by Shapstar on Oct 3:

1) They use an ED element in this scope but they will NOT disclose what that glass type is.
2) Despite some speculation to the contrary in online forums, there is only ONE optical version of this scope worldwide. While some other international dealers state that this scope has an FPL-53 element, Sharpstar itself does not specify this."

 

Clear as mud. Not sure how to reconcile that information with user experiences. 



#75 Barologuy

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Posted 15 February 2021 - 03:55 PM

Clear as mud. Not sure how to reconcile that information with user experiences.


I think the takeaway is consumers that have felt wronged by this are going to seek more information in the future from these companies before trusting them with their money again. At the end of the day though I think the big aspect is the understanding that entry level optics give you entry level photography, and you really can't complain about a little CA at this price point, but driving home the understanding that APO is a measurement, not a binary standard, is important. People get what they pay for. Am I upset about the CA? A little bit, but I'd be lying if I wasn't happy with the scope overall because of a little CA. Consumers need less people like Astrobackuard, and more people who give honest reviews with things people care about instead of hyping these products up. Whoop de doo, every new product *always* fulfills a new purpose or expands on an existing one, but the real question is, and should be asked of every reviewer, is "Does this product do what it sets out to do, better than I could do it without the product or a cheaper product." If the answer is no, people need to hear that. The last thing we need is a larger pool of bad products that already have simple, effective, and sometimes even lazy solutions.
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