Advice please on Canon lens

[carastro]

I have never really done more than a couple of widefield images as I always found getting focus difficult with the kit camera lens.  I don't have the luxury of anything distant to focus on as I am surrounded by houses, so I have been advised to get a fixed focus lens rather than the zoomable kit lens I currently have with my DSLR.

As I am completely ignorant about imaging with anything other than a telescope and don't understand normal photographic language, I'd be really grateful for some advice on getting a fixed focus lens, in particular I don't want to buy anything too expensive at this stage in case I am just as useless with a fixed focus camera.

I have seen this one on Ebay, would this be suitable:

http://www.ebay.co.uk/itm/181535290947?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

BTW I have a modified Canon 450D and want to be able to use it on holidays with one of these mini tracking mounts that are now on the market.

Many thanks in anticipation, and please don't blind me with technical lingo.

Carole 

[alan potts]

I did have this lens a few years ago though I think it was the Mk 1 version. I have to say there was rather too much plastic for me but all my other lenses were 'L' types costing a lot of money so not really a fair comment. Optically it was very good though but not in the same class as I was using. So much depends on what sort of size you want to view images at and in your case I guess it is A4 or thereabouts or laptop size.

I have a funny feeling seeing one of these on AB&S the other day so it may well be worth a try there. I my books with optic you get what you pay for and at this price point you are not getting the highest quality but I am sure it would be good enough for you to start with to see how you get on and if you can pick the same up S/H then so much the better. Sigma are also worth looking at but I found them noisier than Canon on autofocus but I imagine you will manual focus.

Just a thought, they say that 50-55mm is about what we see with our eyes from the point of FOV.

I am sure you will not be unhappy with it for the cost.

[carastro]

Thank you, as I say I just want to see whether I can produce something better than my previous attempts initially, then if I find I am getting reasnaoble results but am limited by my lens I can think again.

Thanks

Carole 

[alan potts]

Carole,

When you are using such a fast lens, F1.8, this is rather quick. The lens when open, this means when the lens is used towards the full F1.8 aperture,  has a very shallow depth of focus. At the other end of the scale say F16-22 the depth of focus, or depth of field as it it know will be massive, something like 5 feet to infinity will be in focus.

If however you focus the camera on the most distant object you can find, make sure it's at least 20m away, then turn off the auto focus or  mark where the focus ring is this should set you in good stead for the night. I am not totally sure this lens has a focus ring but I believe it has, it is a long time ago i had this one. I would also stop the F speed back to 2.8 or F4, this will only help the overall sharpness.

A fairly cheap lens like this will not perform brilliantly at wide open setting (F1.8), to get this you have to spend over 1000 quid new.

Alan

[ronin]

Now I could be wrong but a "fixed focus" lens sounds wrong, I do not know of one produced by anyone.

A fixed focal length yes, they exist and are what I suspect you mean - often called a prime lens, and the one in the link is that.

You will still have to switch it to Manual Focus and then get it focussed by hand yourself.

That one fits the requirements, there are others and you may be advised to go visit a camera shop as they often have them in used.

The one linked is f/1.8 at maximum opening, you would be advised to set it a bit less, say 2.4. What usually happens is at the extreme they produce an image but it improves significantly by making the lens in effect a bit less in diameter.

If your camera is like mine you will have to work out how to set it to a fully manual camera. Really just remembering the 3 settings that have to be made - ISO, Aperture and Exposure length. Then go point at the heavens and let rip. :eek: :eek:

Unfortunately cameras now are not really intended for somone to actually know anything, and certainly not someone wanting to want to do anything different (AP).

The good thing is that you have a button marked Delete.

[happy-kat]

For a third of that price could look to get a vintage prime lens on ebay such as one of the super takumars, fully manual and my 55mm f2 opens really wide and sees loads of stars.

[glappkaeft]

I have never really done more than a couple of widefield images as I always found getting focus difficult with the kit camera lens.  I don't have the luxury of anything distant to focus on as I am surrounded by houses, so I have been advised to get a fixed focus lens rather than the zoomable kit lens I currently have with my DSLR.

Hi Carole.

When people speak of fixed lenses they mean fixed focal length not fixed focus. While fixed lenses are generally much cheaper than an zoom lens of equal quality you still need to focus it.

The kit lens that you have is actually pretty OK to start with. There are three main tricks:

1. The wider the FoW the longer you can shoot before you run into to much problems with star trailing. With a fixed tripod 18 mm should get 20-30 seconds minimum, at 55 around 7-10 sec. For a equatorial tracking mount it depends on the quality of the mount and the accuracy of the polar alignment. With a wide lens you should be able to reach 5-10 minutes easy.

2. Most lenses work better stepped down, try f/5.6 (AV mode or M mode) with the kit lens if the edges look bad.

3. The only good way to focus a camera lens is using the live view. Find a bright star or planet anywhere in the sky, do a rough focus and then change to the 10x mode and do fine focus. Then move to your target and be very careful not to accentually touch the focus ring. As an aside you are very lucky you have the 450D, it was the first Canon camera in that product line with live view.

[Owmuchonomy]

Hi Carol, the lens you have highlighted is a fixed focal length lens also called a prime lens as described above. It still needs manual focussing for AP so if your issue is accurate focussing then you still have to find a way to do that. You have a 450D which correct me if I'm wrong does not have a flip out screen. My 600 D for example does have a flip out screen and live view and this means you can accurately focus in any position by using 10x live view on a star or similar bright object. Therefore if I were you I would consider a camera body upgrade if possible. In addition, kit lenses tend to be zoom lenses and can suffer from zoom 'creep' and as a consequence lose focus easily when perched at strange angles. Hence a prime lens is a good choice with the added advantage they tend to be better quality.

[wxsatuser]

Nifty Fifty........the focus ring is that thin knurled ring on the end, on mine it's very slack, no real feel to it.

It can creep.

I much prefer my nice Sigma/Canon L focus rings that have some feel to them.

Focus as above, with liveview at 10x, you will see the best focus point.

[Psychobilly]

It's pretty good VFM... I tape the focus ring with micropore and use remote manual focus in liveview mode from EOS  Utils or  FWHM  based "Autofocus" from APT...

In a test between the various 50mm lenses that Canon produced they all needed stopping down to around f4 to get decent performace for astro use...

http://www.astrosurf.com/buil/50mm/test_us.htm

Peter...

[carastro]

Thanks for the advice so far every-one. Yes it probably was a fixed focal length I should have said, I told you I didn't know much about the terminology.

How do you step down the lens?

My 450D has an LCD screen at the back of the camera so you can see live view and zoom in on this, so that's not a problem.  

Seems it could well have been my lens slipping then that has caused problems in the past.

Need to digest what you have all said.

Thanks

Carole 

[happy-kat]

I use my android tablet to help focus as I get a 7 inch screen.

Maybe you have an android phone?

[carastro]

Maybe you have an android phone? 

No I don't.  I could use the laptop when I am in England, but I need a portable set up for going abraod.  

Does any-one have experience focussing with a Y mask?  Does it work?

Also how do i tape up a zoom lens without nudging it whilst doing so?

Carole 

[carastro]

This is probably the only image I have done with the lens that i didn't throw away, and even this I think is not focussed properly.  

This was:

30secs x 6 Modified Canon 450D

Mounted Piggyback on ED120  & NEQ6 (whilst I was imaging another object with the telescope and CCD camera).

[Psychobilly]

Does any-one have experience focussing with a Y mask?  Does it work?

Also how do i tape up a zoom lens without nudging it whilst doing so?

Carole 

Y-mask Yes they do,,,

Tape - Carefully... in the past I have also used small blobs of blutack prior to taping... You might want to consider something like the TS Lens microfocus adaptor if you need to focus manually

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3286_Microfocuser-and-focus-lock-fuer-camera-lenses-up-to-D-135mm.html

Peter...

[carastro]

I just tried googling that Peter and also looked on the Telescop service website but can;t find it.  Any chance of a link?

Carole 

[Psychobilly]

Just added it to my previous post...

http://www.teleskop-express.de/shop/product_info.php/language/en/info/p3286_Microfocuser-and-focus-lock-fuer-camera-lenses-up-to-D-135mm.html

Peter...

[carastro]

Going back to my image above.  Could it be I am not "stopping it down" as you call it correctly?  Is that the F speed thingy?

Carole 

[Psychobilly]

i would say you hadn't got critical focus ..  Stopping down helps a bit ...

You need to make tiiny adjustments - not easy by hand which is Why I tend to use remote manual  controlling the camera from a netbook...

Here's a link to a thread from 2011 when I explained how it works,,,

http://stargazerslounge.com/topic/116670-canon-1000d-remote-manual-focus/?hl=%2Bremote+%2Bmanual#entry1154649

If you haven't got  access to  a "computer" those TS gizmos are the next best thing...

Peter...

[carastro]

Great got it.  bit cumbersome, but seems to do the job well.  So if I got this then maybe I could cope with my current lens and a Y mask.  

What size would I need?:

Telefokus 135, Telefokus 105 and Telefokus 75

is it the diameter I am measuring?

Carole 

[Psychobilly]

It depends on the diameter of the lens(es)  that you want to use it with...

[ollypenrice]

The device to which Peter refers is this from TS;

It's the pair of aluminium rings. While it is a fiddle it is a sight less of a fiddle than trying to use your fingers to get a top class focus. I found this effectively impossible and got far better results from the TS device.  This was my favourite;

You can stop down a longer FL lens from the front by making an aperture mask. I'm not sure that this will work with shorter FL lenses but it worked at treat on my 200mm lens. You can buy everything from a graphics store.

Obviously you work out the mask's hole size by dividing the focal length of the lens (in my case case 200mm) by the focal ratio you want to try (I went for F4) so I cut a 50mm hole. These are complex lenses soyou can't  be sure you really are going to get bang on F4 but it doesn't matter. It's no bother to make some slightly different sized holes.

Peter also passed on to me the excellent tip of focusing on the intersection of the 1/3 lines on the chip. (Imaginary lines parallel with the chip sides and a third of the way to their opposite sides.) This gives the best average focus over the chip and is worth noting.

Olly

[carastro]

Thanks Olly.  Well at least it is not just me who has had these problems.  As I say I really gave up on widefield stuff and concentrated on telescope imaging.  But going on a holiday abroad to dark locations I have an incentive to get my act together.

I think I'll probably get one of those and try out a Y mask before spending out on a new lens.

Many thanks, this is a great forum for getting advice.  

But I still don't understand this "stopping down" stuff.  

Is this the "F" stops, and I believe the lower you go the faster it is like focal ratio in telescopes.  

Am I right, if not I really would appreciate an explanation.  

Carole

[Psychobilly]

The trick with the focuser gizmo's is make sure you have it properly centred on the lens - all there locating screws the same length..  When cutting the aperture masks make sure you cut the OD first ...  yes it's effectively the F-stop

[glappkaeft]

Going back to my image above.  Could it be I am not "stopping it down" as you call it correctly?  Is that the F speed thingy?

The only visible problem in that image is bad focus. The focus could be masking other issues but there is no way to tell without better focus.

How do you step down the lens?

You put you Canon camera in Av (aperture mode or M-mode (manual mode) using the big knob that has P, Tv. Av, M etc printed on it. Then the f/number is usually set by rolling one of the scroll wheels (there might be one or more wheels) possibly pressing the Av-button depending on the mode/camera. The exact details vary somewhat between camera models and the different camera modes so you need to look in the manual. Setting a higher f/number is called stepping down.