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Uranium235

Interesting new Astro lens (200mm)

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Hmmm... ive just come across this, astro stuff from Sharpstar occasionally pops up in my feed, which is usually ignored (until proven) - but this one caught my attention:

http://www.askarlens.com/index.php/wap/class1/179.html

Its a 200mm f4 lens, with inbuilt microfocuser (nice touch). And the test images ive seen so far are actually quite good in the corners - that might have something to do with it being f4... so it might not be suitable for someone looking for a photon hoover. And its got just 6 elements in three groups, not nearly as complex as some others (the Sammy 135 f2 has 11 elements in 6 groups!).... whether that is to its detrement.. I dont know. Its too new to comment until Ive seen more data.

Thats the trade off I suppose, swap a bit of speed for tight corners.

The price, I reckon it will be about 800 quid.

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lol... 699 there but once it hits the UK - you can be sure it will be more :D  

However, all the test shots Ive seen are in narrowband - I need to see something in LRGB or OSC to see how it handles broadband imaging.

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For some reason they went for a telephoto design ie the lens is shorter than its focal length.

This has added extra "glass" to the design, and image quality will have been compromised in the search for a shorter lens.

So it will come down to price and performance comparisons with equivalent Canon etc lenses.

Michael

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Yeah, its going to be up against the Canon 200mm L series - which (as far am im aware) cannot deliver a flat field to the corners over APS-C without being stopped down.  So thats the benchmark its got to beat. I guess one other thing going for it is that the flange-sensor distance is a far more comfortable 55mm.

Still need to see how it handles CA though, and that wont come until we see some shots in broadband... M45 would be a good test. Flare tests would also need to be done for any out of shot monsters like Rigel.

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Forgot to mention, its also up against the Redcat from WO - all of a sudden the mid (price) range is getting quite crowded...lol

It would help if we knew exactly what those ED elements were made of. Anything less than FPL53 will not be sufficient.

 

Edit:

Ive asked them directly what glass it is, awaiting a response ;)

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Had a response, but no detail as to what its made of. I guess the proof of the pudding will be in the eating - just gotta sit tight and see what develops (pardon the pun). :D

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3 hours ago, Uranium235 said:

flange-sensor distance is a far more comfortable 55mm

That's including an 11mm T2 adapter, so it's standard Canon 44mm.

Michael

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I am not entirely convinced by this lens, not enough elements for my liking but would like to see a head to head with the Canon 200mm f/2.8 set to f/4 or even the "cheap" 70-200mm f/4 L lens used wide open.

Alan

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Yep, that's why we've got to sit back and let someone else bite the bullet first 🙂

It's not released yet, so I suppose we wont start seeing any images from consumers until perhaps September.

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2 hours ago, michael8554 said:

That's including an 11mm T2 adapter, so it's standard Canon 44mm.

Michael

But it's still 55mm (i believe)  for those who dont want to use the bayonet system (ie: for ccd/cmos). There should be an option for people (like me) who detest bayonet fittings...lol 

There does seem to be a thread on the backend of it, but it's not mentioned whether its M48 or T2 (m48 would be more sensible)

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12 hours ago, Uranium235 said:

But it's still 55mm (i believe) 

Yes I'm wrong, the back focus is 55mm, which with the right adapters will fit lots of cameras, not just Canon.

Michael

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10 minutes ago, michael8554 said:

Yes I'm wrong, the back focus is 55mm, which with the right adapters will fit lots of cameras, not just Canon.

Michael

Yes indeed, you will need that 55mm especially if working with something like a QSI camera - which eats up a whopping 35.5mm at minimum (ws version).

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Hang on a mo.... we've got some movement....

Been offered a tester for review..... need to run this past management - I'll be back in a bit ;)

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16 hours ago, Alien 13 said:

I am not entirely convinced by this lens, not enough elements for my liking but would like to see a head to head with the Canon 200mm f/2.8 set to f/4 or even the "cheap" 70-200mm f/4 L lens used wide open.

Alan

There are a few tests I can do to see how it gets on.

1) Corners (first and foremost)

2) B-mask test (focus on green, then switch between red and blue to see how much movement there is in the diffraction pattern)

3) OSC (use a DSLR to take an image - then split the channels and inspect star size/focus)

4) Reaction to drops in ambient temperature - would be interesting as this lens weighs a whopping 1.8kg

5) Mosaic building capability (it has to be very flat for you to effectively build a mosaic without wasting valuable data)

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Looks like its on guys.... watch this space ;)

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22 minutes ago, Uranium235 said:

Looks like its on guys.... watch this space ;)

Nice one..

Alan

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5 hours ago, Uranium235 said:

There are a few tests I can do to see how it gets on.

6) performance wide open and stopped down

Michael

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3 hours ago, michael8554 said:

6) performance wide open and stopped down

Michael

Oh, I'll be looking to run it wide open all the time ;)  whats the point in imaging at a speed slower than its maximum? If youre paying for an f4 flatfield, you expect it to be flat at f4 - no messing about required (thats what people want to know).

I remember getting the f2 Samyang because it was flat at f2, not because I wanted to slow it down :) 

Though it might be worth taking it up a couple of stops, cant see there being that much difference if its already flat over APS-C (at f4)... perhaps slightly tighter stars but thats about it.

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On 10/08/2020 at 16:53, Uranium235 said:

Incoming.... watch this space... ;)

Is it here yet? :)

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I'm using 200mm f4 lenses for AP but these are vintage SLR lenses and bought second hand from a well known auction site for very little.  I use them at full aperture on 4/3" sensor cameras.  They are sharp well up into the corners as are all the Asahi(Pentax) Super Takumar or SMC Takumar lenses I use.  One difference from that $700 jobby is that terrestrial lenses are not fully APO right into the deep red but with narrowband this doesn't matter - just that the focus at OIII wavelength is a bit different from Ha or SII.

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4 hours ago, Coco said:

Is it here yet? :)

Its been here for a while mate :D

 

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