Canon 200mm F2.8L vs. Fast Refractor

[Macavity]

Heheh. Thus far, I love my (non-IS) f/4 70-200mm. Clearly, none of my scopes

go below f/4 without (dubious!) focal reduction. Just learning m'self too, but:

http://www.the-digital-picture.com/Reviews/Canon-EF-70-200mm-f-4.0-L-USM-Lens-Review.aspx

The Canon EF 70-200mm f/2.8L IS II USM Lens is a GREAT upgrade from the 70-200 f/4 L, but only if you need f/2.8 (lets twice as much light in) and/or IS - or weather sealing (the 70-200 f/4 is not weather sealed). You will not find the IS version's image quality to be much better - Full frame corner sharpness is better on the IS lens until the end of the focal length range where they equal out. The f/4 version performs better than the IS lens with Canon Extenders when used at the 200mm setting until both are stopped down to f/8 or so. [] The IS version carries significantly more weight and costs much more than the smaller f/4 version.

I decide to forgo f/2.8. I didn't need the image stab.

I think the PRICE dictated much of my choice tho! 

You could always stop down the f/2.8 aperture with

an adapted *circular* 2" filter to avoid diffraction.

Maybe you get the best of all worlds that way...

[robertm]

The main reason for stopping down is to avoid use of the glass around the edge where lens design is most compromised. I'm afraid the trade off is to make the lens a bit slower but that depends what the use is. The 200L II is definitely good for f/3.2 narrowband but for broadband (I.e. luminance) then I suspect the f/4 that has already been mentioned is where the sweet spot is. One thing to note is that at f/4 you are only using 200/4 = 50mm of aperture and that's within a knat's of a 48mm threaded filter. Also if you use a threaded filter then, as well as the f/4 stop, you won't be troubled with awful diffraction spikes.

I've not used the 70-200 so can't comment.

One new lens of mine is that Samyang 35mm f/1.4, live view with the A7s is absolutely astonishing. It does need to be stopped down a tad to around f/2 for that sensor size but an APS camera might be able to use it opened up a bit more. I've had a few bad samples (sent back to Amazon) so you need to take a critical look to make sure the aberrations are symmetrical.

Robert

[ian_bird]

I don't know. It might be tight to get a F/W in there but I think someone (Gerd Neumann, maybe?) made a slide drawer for CCD to camera lens. This is only going to work sweetly for CCDs with very small pixels. I used a Geoptik CCD-Lens adapter and it can take filters, but involves a full disassembly to change filters. I know someone who's done this but it would be a step too far for me. Cameras with integrated filterwheels (QSI and some Atiks) might have a short enough backfocus requirement. In fact I think they do but this would need checking.

Olly

Hi Olly

Were you using the Atik 4000 with the 200m Canon when you felt that the pixels were too big? I have both - I was going to give them a try - but if you don't think they are a good combination I might give it a miss.

Out of interest - how does having too big a pixel size show up in the image? Or to put it another way - how can you tell?

Cheers

Ian

[Tommohawk]

The main reason for stopping down is to avoid use of the glass around the edge where lens design is most compromised. I'm afraid the trade off is to make the lens a bit slower but that depends what the use is. The 200L II is definitely good for f/3.2 narrowband but for broadband (I.e. luminance) then I suspect the f/4 that has already been mentioned is where the sweet spot is. One thing to note is that at f/4 you are only using 200/4 = 50mm of aperture and that's within a knat's of a 48mm threaded filter. Also if you use a threaded filter then, as well as the f/4 stop, you won't be troubled with awful diffraction spikes.

I've not used the 70-200 so can't comment.

One new lens of mine is that Samyang 35mm f/1.4, live view with the A7s is absolutely astonishing. It does need to be stopped down a tad to around f/2 for that sensor size but an APS camera might be able to use it opened up a bit more. I've had a few bad samples (sent back to Amazon) so you need to take a critical look to make sure the aberrations are symmetrical.

Robert

I looked at other brands, including Samyang and Sigma, and surprisingly the Tamron 70-200 seems to de well in reviews. Noisy and erratic AF, but I don't need that. Non-weatherproof body, but plastic so less condensation maybe.

Anybody have any expereince with Tamron lenses? 

[robertm]

I think this is where experience comes in. A lot of lenses look superb for terrestrial but as soon as you look at the bright pinpricks that are stars then that's where you see astigmatism, coma and chromatic aberration rear themselves. The last thing you want is a compromised image before processing even starts (that's my personal opinion).

[thenews24]

I personally love the 200mm f2.8, which I always shoot wide opne. With the help of a microfocuser, I can get sharp, pinpoint stars edge to edge. I am currently using the lens coupled to the Atik 314. Although this is not the ideal combination in temrs of image scale, I can still achieve nice round stars and the FOV is decent. When m tired of using ccd's, I'll throw the lens on the DSLR for some really wide views, and the reults are superb. For under $1,000 USD, this lens is the best option for fast, wide field imaging on a budget, although the geoptik adapter will add to the cost.

Here's my setup. I guide with a 400mm f/5 orion shortube. It is overkill really, but by inmaging at half of the guide FL, i can get up to 20- 30 min subs no problem.

 

[ollypenrice]

Hi Olly

Were you using the Atik 4000 with the 200m Canon when you felt that the pixels were too big? I have both - I was going to give them a try - but if you don't think they are a good combination I might give it a miss.

Out of interest - how does having too big a pixel size show up in the image? Or to put it another way - how can you tell?

Cheers

Ian

Hi Ian,

Yes, I used the 4000 with the 200mm Canon. At the time I had OSC 4000 and mono 4000 so I tried Ha from the mono and 0SC (RGB) from the OSC. I did a wide M45 with just the OSC, too.

The coarse sampling rate shows up in a loss of fine resolution and, more importantly, perhaps, in a blocky look so far as the stars go. If you keep the image presentation size small it is bearable but you can't offer the results at full size. In the end I regarded these results as interesting and as an inspiration to come back at a finer pixel scale and multi panel mosaic.

I'm trying to link to a couple of images I did with this setup but the net won't play. Sorry about that. I image (as do a lot of people) at 3.5 arcsecs per pixel with the FSQ106/Kodak 11 meg combination. That is about as coarse as I ever want to go, I reckon.

Olly

Edited December 5, 2015 by ollypenrice

[Macavity]

With the help of a microfocuser...

Can I ask (generally) which microfocuser is being used? (Link, possibly)

Aside: Rather going off the idea of fitting the (otherwise excellent) TS filter

slide behind the Canon. Might be a good place for the focusser though!

(At the moment extra slide deliveries keep receding into the future)

[Davey-T]

Think it's this one in the above pic

Dave

http://www.teleskop-express.de/shop/product_info.php/info/p3284_Microfocuser-and-focus-lock-fuer-camera-lenses-up-to-D-105mm.html

[topgearuk]

That's the same as the one I've just purchased, but back ordered for a couple of weeks.

[Macavity]

Ah, so that's where the focussing is hiding. (Doh!)

Quite a nifty idea, given the limited back-focus...

I'll have to see if merely "clamping" suffices.

[thenews24]

Ah, so that's where the focussing is hiding. (Doh!)

Quite a nifty idea, given the limited back-focus...

I'll have to see if merely "clamping" suffices.

A Bahtinov mask helps. This was shot with the 200mm f/2.8 with that microfucser and bahtinov mask. Even with a HA filter in the train, I can get nice diffraction spikes with enough exp bin combo:

foucisng 200mmf2.8withmask.wmv

[Tommohawk]

A Bahtinov mask helps. This was shot with the 200mm f/2.8 with that microfucser and bahtinov mask. Even with a HA filter in the train, I can get nice diffraction spikes with enough exp bin combo:

foucisng 200mmf2.8withmask.wmv

Hey thats nice, thanks for posting. I was going to ask if you're mono or colour, and where does your Ha filter go? Also, It looks like youre not using the Geoptik as a support, so how is the camera/lens supported? Using the lens support foot?

[Davey-T]

I have one of these.

Dave

http://www.iankingimaging.com/show_product.php?id=1378

[thenews24]

Hey thats nice, thanks for posting. I was going to ask if you're mono or colour, and where does your Ha filter go? Also, It looks like youre not using the Geoptik as a support, so how is the camera/lens supported? Using the lens support foot?

I do use the Geoptik. Here's a quick video of the adapter to lens, with 1.25" HA filter threaded in. You can use 2" in this adapter if needed.

geoptik_to_lens.wmv

[Tommohawk]

Well, here's the latest. I did a bit or reading up and discovered that the latest of the Tamron F2.8 300mm lenses (360B version) gets good reviews on a par with Sigma and close if not quite as good as the Canon.

Difference is I got the Tamron in good order for a jot under £300, where the Canon is... well, lots more.  So whether this was a good move remains to be seen. I'll post some pics as soon as I can.

One other advantage of the Tamron is I can save some back focus by fitting an M42X1 type Adaptall mount, and fit a 42x1 internal and 48mm external adatper which will screw straight into 2" filter wheel - this saves the width of the Canon to CCD adapter ie about 14.5 or 17mm depending on type. Allowing for a 3mm locking ring this uses 3mm back focus, filter wheel is ~20mm, camera connector is 17.5 if connected direct which leaves me 3.5mm to play with for a total of 44mm.

Does that sound OK? 

Next problem is this requires a 2" filterwheel where I probably only need 1.25", so starts to get expensive for filters. And to make matter worse, at F2.8 I may need spooky fast NB filters.

So the next techy question please is, what do people think about NB for F2.8? The Baader F2 set are £499 which is a bit stiff. Any thoughts on this please? Can you maybe put a 1.25" casette in the 2" wheel?

[Knight of Clear Skies]

Hope the new lens works out well, would be interested to hear how it performs. Regarding the filters I'd suggest testing it out first - if you find you need to stop it down anyway you could buy the cheaper set.

[Tommohawk]

OK I got the F2.8 300mm Tamron lens about 10 days back, but a few hiccups and pants weather has made testing slow.

First off the glass was in good shape, and the lens casing generally good too, but there was something slightly loose in the coupling to the camera. Not much play, but enough to prevent reaching infinity. OK for about 300m, but not OK for the moon.

I thought this was just the adaptall mount initially, but closer inspection showed it was the back end of the main lens itself. The rear adapter ring is (should be) secured with 3 small screws which were loose, and I could see that the latch which fastens the adaptall mount had a return spring which was adrift. Nothing that a few nervous moments with a good light, a screwdriver, and a ready supply of expletives wouldn't fix.  

All sorted, so had a preliminary test just on a tripod. Overall I'd say the lens performs well, but there is some chromatic aberration for sure. On bright - overexposed - shots of the moon, it was quite visible, but with normal exposure couldnt be seen. But man, focusing is a pig! I can see why you folk go for the spooky TS focuser now.

Anyhow here's test cropped lunar shot - done at F2.8, 100 ISO, and only needed 1/2000 sec exposures! Best 15 out of 26 stacked with Avistack. The wavelets were overdone a bit but its just a test for CA.and generall performance when set at F2.8.

I cant see any CA but then my colour vision is poor. Maybe I should stick with a doublet.... or maybe a singlet!

Remains to be seen how it will perform on DSOs - need to get it fixed to the HEQ5 for that. I plan to get a Duomount type set-up so I can leave the guide-scope in place and use 200PDS or Camera as required.

Any comments/criticism welcome! 

[Macavity]

Might be of interest... (if you made a significant "profit" over Christmas!)  

Article in Astronomy Now (Jan 2016): "The Ultimate wide-field Refractor"

The Canon EF 200mm f/2.8 L II USM + Canon cam, Starlight Xpress etc.

[Tommohawk]

Might be of interest... (if you made a significant "profit" over Christmas!)

Article in Astronomy Now (Jan 2016): "The Ultimate wide-field Refractor"

The Canon EF 200mm f/2.8 L II USM + Canon cam, Starlight Xpress etc.

OK thanks for the heads - up. Funny thing is I have AN on subscription and haven't looked at the latest issue just yet. I'm still catching up with "The sky at night this month".... for October!

[daisy74]

Hi! I am quite new on this, I took the opportunity to take a look these days into some nice lens because of the current situation (not so much to do, tbh). I found a pretty nice list of lens of canon compering some prices, and because you guys looks pretty experienced on this, after reading this thread, I would like to know your opinion about which one is recommended, thanks!

P.D: I have a budget around 500 and 2.000 dollars

[Knight of Clear Skies]

4 minutes ago, daisy74 said:

I would like to know your opinion about which one is recommended, thanks!

Probably top of the list is the Samyang/Rokinon 135mm f2, there are lots of example images in this thread.

[daisy74]

wow, so fast, thanks