Camera lens, is this right? (know your lenses?)

[Aenima]

Do you know your lenses?

Because I don't, and this is a tentative attempt at widefield. I went to the trouble of getting a nikon lens for a nikon camera and one which said it focuses infinity, else all kinds of problems might have come before I got started.

But after piggy backing my camera on my mount and turning focus to infinty, manual mode with release, I looked at the preview and noticed quite bad coma - on a camera lens this is unfamiliar to me so please could someone take a look at these shots for me?

No processing: ~100mm

between 6 - 20 secs ISO 800 - HI-2

Coma this bad isn't what I was expecting, especially on a nikon lens. It may have been slightly cheap but - is this normal?

How can I choose one which doesnt coma?

Any help hugely appreciated.

Regards

Aenima

[nmoushon]

Coma like this is normal with the cheaper end of camera lenses. My stock camera lenses on my Canon has the same problem. You have to go up in lens quality (and price) to completely get rid of coma.

[Aenima]

Thanks it was completely new and a shock to me that coma would appear on anything other than my badly collimated reflector!

So, can II assume that for a nikon 28-100mm AF-g nikkor, this level of coma is absolutely normal?

Would anybody suggest a reasonable priced lens that will achieve decent widefield shots, or at the least whether processing or using other kinds of techniques might help the current lens cope better?

Much appreciated nmoushon, thank you.

[nmoushon]

I'm not lens savvy so I couldn't point you to a specific one. The coma comes from the fact that the cheaper lens dont deal with the point sources lights that well.

Also what are you looking for in a lens? A wide angle lens or a telephoto lens or something in the middle? Also a zoom lens or a fixed lens? Fixed lenses tend to be better quality and better for AP than zoom lenses but not necessarily cheaper. A popular one is nick-named the nifty fifty which is a fixed 50mm lens.

[Steve Ward]

All lenses focus past infinity , do not rely on the end-stop ...

Liveview on , put a bright star a third of the way in from the edge of the preview screen , zoom in X 10 , then focus.

Would be easier tethered to a laptop but I'm assuming you don't have that facility with the 3100.

[chiltonstar]

I've found sometimes that it's easier in practice with an old, fixed focal length lens (cheap these days). I use a manual Nikon 50mm f1.8 lens which, as it is a manual lens, has a more accurate "infinity" position on the focus scale than a typical autofocus lens. I stop down two stops to f4 - that then gives pin-sharp stellar images with my D300.

Chris

Chris

[Polar Bear]

As others have said, don't go by the infinity marking on the lens but instead rely on manual focus with the preview at max magnification.

Standard fixed focal length lenses will perform better than inexpensive zooms. The Nikon E series lenses are good performers for the price if budget is limited.

Alternatively the 50mm F1.8 Mk 2 Canon for your EOS 300D will give good sharp results.

Paul

[ronin]

You may have been better with a prime lens, a 28-100 has to deal with all the focal lengths between 28 and 100 and simply they cannot do all of them well.

Another thing is I do not know of any zoom lens F1-F2 that performs better at F2, which seems a little odd as no-one really buys one to use at the shorter focal length. Just about every zoom lens is described as soft at the longer focal length.

You would probably get a better image if you set it to 65mm or 70mm and you could also stop it down by 2 steps. The old 80mm portrait lens comes to mind. Oddly a lens that was intended for a 35mm camera would be better as the edge of the image falls off the sensor and so there is less curvature/coma present on the sensor itself.

I think dpreview does a good analysis of just about all lens, have a search and see what is said about yours.

If you want sharp then it will cost, I was speaking to someone with a Nikon camera with a nice lens they used for birding. In simple terms the lens alone cost more then my car (VW Passat). Did get some nice images however.

[Polar Bear]

If you want sharp then it will cost, I was speaking to someone with a Nikon camera with a nice lens they used for birding. In simple terms the lens alone cost more then my car (VW Passat). Did get some nice images however.

This is only true if you require long focal length combined with a big aperture and fast AF, EOS 300mm F2.8 / 400mm F4.0 etc.

Standard lenses like the EOS nifty fifty are sharp and only costs £89.00 new.

I use a Pentax Super Takumar 300mm F4.0 from the 1970's on my EOS bodies and it is as sharp wide open as L series lenses. Cost £35 with the adapter !

Paul

[chiltonstar]

This is only true if you require long focal length combined with a big aperture and fast AF, EOS 300mm F2.8 / 400mm F4.0 etc.

Standard lenses like the EOS nifty fifty are sharp and only costs £89.00 new.

I use a Pentax Super Takumar 300mm F4.0 from the 1970's on my EOS bodies and it is as sharp wide open as L series lenses. Cost £35 with the adapter !

Paul

I've got a manual Nikon 300mm f4 lens which is a cracker - that didn't cost me very much either!Chris

[Dave]

The lens, even a zoom type, will focus, but not where infinity is marked on the barrel.

This is the case regardless of the cost of the lens being used.

Then once you've got the sweet spot, lock it with a piece of tape to stop the focus ring moving.

You can get good images, it just requires a bit of perseverance.

Dave

[Aenima]

Huge thanks for all the replies.

Unfortunately without a scope attached i'm rather a newb at cameras, and although its a nikon lens which has the theoretical ability to reach infinity this one doesnt, nor did the telephoto m42 200mm one I tried before it. I have trouble believing that all lenses do focus infinity for the simple reason that out of 5 ive tried, 4 of which I have now only the kit 18-55 does so. I understand the newer ones do go past infinity for - I believe - flexibility at differing f-lengths etc. but not only does the lens not have it marked but it has a hard stop just before distant objects and points of light reach sharp focus, in fact the 28-100mm stops at a point where stars still look like donuts, I spent some quality time with the EQ5 and manual focus with both nikkors - live view is good on bright stars but I really wanted to see the smaller ones as well because the brighter stars can appear as points with enough exposure or flare as the hole in the 'donut' gets filled in regardless of it being a ring and not a dot.

My industar 50 goes nowhere near infinty but that wasnt expected to, also my Canon-fit tamron 70-210 stops dead just before the end of its inward travel, which logically should be near infinity but it just doesn't quite reach, there might be a solution there in the form of an adapter - inward travel can be adjusted slightly by thinning down the bayonet adapter to bring the lens rear closer to the sensor. Not for the nikkor though as it goes direct into the camera. It has the oo mark on it, but not as a guide just as a label that says it does 0.96" - oo near the serial number.

Anyway, long story short - I just want a lens that gives infinity at about 80 to 200 mm or either for widefield - the 18-55 is ok but not much magnification to it.

Many thanks for the suggestions everyone posting above - the fixed lens looks like it would be worth a better look.

I took quite a few pics in my fiddling tonight and will check them more thoroughly and maybe post an example or two - never know it might help.

Thanks again,

Regards

Aenima

[Aenima]

Is it me? The camera is nikon. The lens is nikon. The lens has infinity marking (marking, not marked, it just says oo it on the back) and it wont turn enough in the desired direction to reach infinity.

I would dearly like to think its a fault or bad luck, but the lens is ok - aside from the coma - in every other way, it just doesn't turn far enough for distant focus. O.o

I hope its not the camera, thats for sure.

Regards

[CedricTheBrave]

I have a Nikon D7000 with a 28-105, 70-300 and a 50mm prime.

the zoom lens are not marked at infinity but you take it to the stop and back a few mm and that will be it

the 50mm prime has a marker which is just before the stop.

all work ok

[Aenima]

Thats encouraging news, thank you. I have tried the 'go to the end and back a bit' but the donuts just get slightly bigger not smaller, and to look through the viewfinder its clearly not passing 'through' infinity - like the kit lens does - as the distant objects do not get sharp then soft again - like the kit one - which would suggest that the focus just doesn't quite get there - again, the 18-55 lens is able to all the way from almost a foot away to infinity and then slightly past, looking through the VF you can see this happening aas focus travels from close to distant to just past sharp at the other end. Unfortunately the 28-100mm goes from close to almost sharp at the other end.

I know it seems like i'm not getting that the infinity point is back a bit from the end but after trying this on stars it really seems like the end is as far 'away' as its going to get.

I'm going to try a post about widefield tecniques and lenses, hopefully it might shed some light on exactly what I should be trying and how to choose the right lens. Someone somewhere must have a d3100 and use it for widefield.

Thanks t those who posted above, grateful for any input.

Regards

Aenima