39 replies to this topic

[Astrojedi]

Ok so I pulled the trigger on the new Askar 200mm F4. Here are the details in case you are wondering. http://www.askarlens...class1/179.html

 

In this thread I will post my thoughts and results from the evaluation of this lens for others who may be interested. I have no relationship to the vendor. I have never purchased any other product from this brand or parent company Sharpstar before so was not quite sure what to expect.

 

I ordered the lens (I guess that is what we should call it) from Agena Astro and it arrived yesterday - very impressed with the quick shipping. Even though the Moon was out in full force the skies were clear so I could do an initial test of the performance. Here are my initial observations:

 

Very well built and heavy! Weighs 4lbs - heavier than the RedCat although it is pretty compact. I purchased this lens primarily for my wide-field and remote imaging setup to use with my Canon Ra. 

 

It is much larger than it looks in pictures - see picture below for a comparison with my Canon 70-300 zoom lens which looks pretty light and small in comparison

 

Next post will be first light results...

 

 

 

Edited by Astrojedi, 04 September 2020 - 01:45 PM.

[Astrojedi]

First light... kind of...

 

Surprisingly it was clear last night so of course I had to try and test the lens out. Unfortunately, it was close to a full Moon so no serious imaging but my goal was to test the correction of the lens over a full frame sensor.

 

I setup the lens with my Canon Ra. I used the EF lens adapter plus a M48 t-adapter. I did not use a filter as I wanted to properly evaluate the full field correction and CA if any of the lens.

 

Here it is setup with the Canon Ra:

 

 

 

 

[petert913]

Looks nice.  Where did you buy it?

[nicknacknock]

Nice! I look forward to reading how it performs when you put it through its paces!

[RajG]

Looks good, but I'm surprised it is so large and heavy. The front filter size is 82mm, which is huge given that the effective aperture is only 50mm. I wonder why - perhaps to reduce vignetting and get more even illumination across a full-frame sensor? For comparison, the Samyang/Rokinon 135 f/2 has a front filter thread of 77mm, while the clear aperture is 67.5mm, but it does vignette strongly at f/2 (easily correctable with flats).

[Astrojedi]

Looks good, but I'm surprised it is so large and heavy. The front filter size is 82mm, which is huge given that the effective aperture is only 50mm. I wonder why - perhaps to reduce vignetting and get more even illumination across a full-frame sensor? For comparison, the Samyang/Rokinon 135 f/2 has a front filter thread of 77mm, while the clear aperture is 67.5mm, but it does vignette strongly at f/2 (easily correctable with flats).

Yes, I have used the Rokinon 135mm quite a bit. I usually use it at f2.8. It is much lighter compared to this lens. The Askar is all metal, even dew shield is metal. Very well built but yes, I do think it could have been lighter. But in my opinion this lens competes more with the Redcat 51 and not the 135mm.

[Astrojedi]

Ok so here is the correction at the edges. This was a 10s full frame image of the NGC7000 area but the nebulosity was completely washed out by the near full Moon. But this quick test was just to get a first look at the optics. I am going to put the lens through its paces a bit more before I draw any final conclusions.

 

Based on this initial image the lens seems to be super sharp edge to edge with zero aberrations. A separate shot of Deneb did not show any CA as well. For some reason I cannot find that image on the SD card or on the PC (I was using BackyardEoS). Between the camera and the software there are about a dozen settings that I need to be mindful of as I use the camera for daylight photography as well. I am sure I missed something.

 

I will take a few more images tonight and evaluate vignetting and performance on bright stars along with further tests on edge correction.

 

Askar 200mm F4 with Canon Ra full frame. Used PI to inspect frame.

 

Edited by Astrojedi, 04 September 2020 - 03:22 PM.

[RajG]

It would be interesting to see how this compares to the well-regarded Canon 200mm f/2.8L, which costs the same, but weighs half as much.

[Astrojedi]

It would be interesting to see how this compares to the well-regarded Canon 200mm f/2.8L, which costs the same, but weighs half as much.

I don't have the 200 f/2.8 anymore but based on first impressions this seems like a much better corrected lens. But the even bigger differences in my view are mechanical. I prefer the M48 mount as well as a 2" filter thread which allows me to reuse my 2" filters and avoid buying additional clip-in filters. I don't think the l-enhance is available as a clip-in. Plus I can use it with my astro cameras without any additional adapters and rings.

 

I also like the very rigid dovetail. I have never liked the lens hanging off the camera. Having said that I would have liked if the Askar 200mm were a little lighter. I would still prefer the Canon lenses for daytime photography.

Edited by Astrojedi, 04 September 2020 - 06:49 PM.

[RajG]

I don't have the 200 f/2.8 anymore but based on first impressions this seems like a much better corrected lens. But the even bigger differences in my view are mechanical. I prefer the M48 mount as well as a 2" filter thread which allows me to reuse my 2" filters and avoid buying additional clip-in filters. I don't think the l-enhance is available as a clip-in. Plus I can use it with my astro cameras without any additional adapters and rings.

 

I also like the very rigid dovetail. I have never liked the lens hanging off the camera. Having said that I would have liked if the Askar 200mm were a little lighter. I would still prefer the Canon lenses for daytime photography.

 

Thanks. You're right, this looks like a good alternative to the Redcat.

[Astrojedi]

Askar first light with the Canon Ra:

 

https://www.cloudyni...mm-f4-canon-ra/

 

 

[B 26354]

Wow. That is really impressive! Thanks for posting about this lens.  

[deepanshu29]

Hi Astrojedi, I am thinking of getting this lens however I have some questions, would be a great help if you can answer.

 

• Does the dew shield or the front element of lens moves when you adjust the focus? Like RedCat moves the front element out. But Canon L lenses do not move the front element. I use LED panel to take flats and generally place them directly on the dew shield. If front element is moveable it shifts the focus, rending flats useless. 
• Have you tried the lens at stepped down aperture? Is there any reason to step down for astro? I came across few tweets from Japanese folks who were using this lens at f/5.6 but I could not find any reason why? How does flat look at f/4?
• Can you share a RAW sub from your EOS Ra? I will be using it with Ra and QHY367c, so it will help to see the stars. Would also be excellent if you can share master flat. 

Thank you! 

[Astrojedi]

Hi Astrojedi, I am thinking of getting this lens however I have some questions, would be a great help if you can answer.

 

• Does the dew shield or the front element of lens moves when you adjust the focus? Like RedCat moves the front element out. But Canon L lenses do not move the front element. I use LED panel to take flats and generally place them directly on the dew shield. If front element is moveable it shifts the focus, rending flats useless.

No the dew shield or the body does not rotate when focusing. The microfocuser is very smooth and precise - very easy to get precise focus.

• Have you tried the lens at stepped down aperture? Is there any reason to step down for astro? I came across few tweets from Japanese folks who were using this lens at f/5.6 but I could not find any reason why? How does flat look at f/4?

No need or reason to step down aperture for astrophotography. Stars are super sharp across the full frame at F4. I tried stepping down the aperture but when you do that the aperture blades move into the light path and it creates spikes on bright stars (similar to camera lenses). So I would only do that for daytime photography.

• Can you share a RAW sub from your EOS Ra? I will be using it with Ra and QHY367c, so it will help to see the stars. Would also be excellent if you can share master flat. 

Flats are on my to do list. I am lazy. I have not used any flats so far with this lens. Illumination seems pretty even. I may need flats if I image from my heavy LP backyard as gradients become more challenging. Let me go dig up a CR3 file.

 

Thank you! 

Edited by Astrojedi, 08 October 2020 - 01:33 PM.

[deepanshu29]

Thank you for getting back. This is excellent. Can you also confirm that the dew shield / lens front element does not move linearly when you adjust focus? 

 

Looking forward to see CR3 files. 

[Astrojedi]

Thank you for getting back. This is excellent. Can you also confirm that the dew shield / lens front element does not move linearly when you adjust focus? 

 

Looking forward to see CR3 files. 

Not sure I understand the question. When you use the coarse focus ring the main lens the body moves forward (almost at the center of the lens). When using the micro focuser I cannot discern any movement - likely too small. This would be true for any telescope and most lenses (except moving mirror designs) as I am not quite sure how else you achieve focus in a lens based system.

[deepanshu29]

Umm let me rephrase - does the dew shield moves in the direction of arrows in image below when you use the coarse focus ring? 

 

 

Some lenses move their front elements / hood when focusing, some don't. For example, Sigma Art series does not. All focusing elements are internal. 

 

Why this matters? - I take flats using LED panel, in field. I point my scope to zenith and just place the the LED panel on top of dew shield. It is not a heavy panel but it is enough weight to move the focus point for the lenses which moves the front element with focuser. It is not a deal breaker but need to figure out a workaround to make sure focus point does not shift when I place the panel on top. 

[Astrojedi]

No that part does not move. I have only seen the front move on Canon Zoom lenses when changing the focal length not while focusing. But I am sure there could be other lenses out there  that work differently.

[B 26354]

Not sure I understand the question. When you use the coarse focus ring the main lens the body moves forward (almost at the center of the lens). When using the micro focuser I cannot discern any movement - likely too small. This would be true for any telescope and most lenses (except moving mirror designs) as I am not quite sure how else you achieve focus in a lens based system.

Perhaps it would be useful as an answer to deepanshu29's question, if you provided two more "side-view" photos like the one in your post #2... one with the lens at "infinity" focus, and one with the lens at closest focus, so that he can see the difference in overall length.  

[deepanshu29]

No that part does not move. I have only seen the front move on Canon Zoom lenses when changing the focal length not while focusing. But I am sure there could be other lenses out there  that work differently.

Great. Actually from the photos it does look like that dew shield part is always stationary. Good to have this confirmed. 

 

I will wait for your CR3 drop before I place my order. Thank you again for answering all these questions. 

[deepanshu29]

Perhaps it would be useful as an answer to deepanshu29's question, if you provided two more "side-view" photos like the one in your post #2... one with the lens at "infinity" focus, and one with the lens at closest focus, so that he can see the difference in overall length.  

Ha ha, that could help. But I think I got my answer  

[Astrojedi]

Perhaps it would be useful as an answer to deepanshu29's question, if you provided two more "side-view" photos like the one in your post #2... one with the lens at "infinity" focus, and one with the lens at closest focus, so that he can see the difference in overall length.  

 

I didn't realize I did something wrong in asking for clarification on a question I didn't understand so I could be more efficient in answering it.

 

You may not value my time but I assure you my sole purpose in life is not to answer questions on CN

[B 26354]

I didn't realize I did something wrong in asking for clarification on a question I didn't understand so I could be more efficient in answering it.

 

You may not value my time but I assure you my sole purpose in life is not to answer questions on CN

I'm not sure why you think that my simple and completely sincere suggestion deserved such an utterly rude and completely inappropriate response from you. Nor do I understand how you could possibly have interpreted my suggestion as indicating that you'd done something "wrong".

 

You, however, do seem to somehow inexplicably feel as though my suggestion for a way to further clarify deepanshu29's concerns was wrong.

 

Considering how much time you'd already obviously invested in offering information and answering questions in this thread, your final comment to me is not only inappropriate and rude... it's frankly incomprehensible.

 

At this point, if I were able to delete my post #12, I would.

[nicknacknock]

People, always keep in mind that something is lost “in translation” when we type stuff, so don’t take it personally.

No harm done, let’s put this behind and chat more about this lens. I got the ASKAR FMA180 myself and I am wondering if the 200 would be of interest, so please, keep this excellent thread going for the rest of us!

[Astrojedi]

I don’t see how my response was rude. It was factual. 
 

It is not about your intentions. You are being presumptuous that I have the time to take pictures two ways and post it here in the hope that is what he is asking without clarifying... I don’t, as it requires me to go down to my observatory in the middle of my work day and take the scope off the piggyback rings (it is mounted on top of my EdgeHD 11), disassemble the setup, take pictures and put all back together again.

 

I rather avoid that and seek clarification in case it is something I can answer quickly. Let’s move on.

Edited by Astrojedi, 08 October 2020 - 10:30 PM.