A question about filters and my "new" lens...
 

Hi,
As some may know, I've been attempting photos of stars...
I decided the best thing to do would be to buy a wide angle lens. I saw a Sigma 10-20mm f4 lens for a good price and bought it.
I know its not especially fast, but I have to work to a budget.
It turned up and was immaculate. It had also been fitted with a filter of the brand "camlink."

Now I've noticed two things.

First up, the lens. When taking regular photos in daylight, I have to have a very low shutter speed, when compared with my other lenses. Is this normal with a wide angle lens?

Second question which is specific to the filter.
Last weekend I went out at night and the front of the lens misted up over the filter. This has never happened for me before. (I usually use Hoya or Gobe filters.)

So do cheap filters (camlink) tend to mist up easily? Do better quality filters have some anti fog coating??

Hi, Jeff (coolcat) and Alan (clf) are the two I know of to ask.
I try to keep to Hoya filters, a bit more expensive but has very good reputation.
Ken.

Hi Ken,

Thank you, I too prefer Hoya, but still impressed with my Gobe ND filters.

I wouldn't have bought the camlink myself, but it was already fitted.

Take the filter off ... and bin it. what type of filter is it anyway? if it's affecting daylight exposures by more than 1 stop there's something wrong unless it is an ND Being supplied with the lens I'd guess it would be a UV filter? A wide angle lens in daylight I'd expect to let in more light (than a longer lens) and so need less exposure - not more. Taking star shots It's not going to make any real difference to exposure - just capture more stars, making the starfield in shot look denser than with a zoomed in lens. Are you using a tracking mount? Found a great youtube vid here includes a diy tracker - https://www.youtube.com/watch?v=vg3a0I0duMI

If the ambient temperature is low then one is advised to expose the camera and lens and give it time to cool and adapt before use; that should reduce the misting.

Hi,
I'd already decided to replace the filter with a Hoya, which I ordered yesterday.
I didn't see any plus point regarding the filter when I bought the lens, other than this cheap filter had been fitted from new and had therefore probably protected the lens.
I have been quite unimpressed with the lens for day light shots and had kind of assumed it was down to the cheap filter.

For star photography I am quite pleased with the lens, just wish I didn't have to use such high ISO, which results in so much post processing...
I'm not using a tracking mount. I'm purely a novice and stare at the sky until I can see things!
I tend to use 3200 ISO and a 20 second exposure.

These are the two most recent results using my "new" lens, both taken with full moon which isn't ideal..

I will definitely check out the video you linked to tomorrow, but now I have to go to bed!
https://farm2.staticflickr.com/1912/...7dfe2eaf_c.jpgStars over the Brecon beacons. Wales, UK. by Philip Davies, on Flickr
https://farm2.staticflickr.com/1916/...73de26a6_c.jpgStars over Ravensroost wood, WIltshire, England. by Philip Davies, on Flickr
Hi, I understand that, I was out with my fiance and her camera was completely unaffected, only mine misted up. It wasn't cold out either.
I assumed that the cheap filter that came with the second hand lens was to blame. I wondered if the cheap filters weren't anti fog coated... (I have no idea if any filter has anti fog coating!)

There is no anti fog coating, at least none that I have ever heard or read about. Lenses though are prone to dampness (think mould and fungus). I would always avoid using a filter of any kind on an 'ultra wide' lens for fear of vignetting and flare. 'Ultra wides' are prone to flare as the light waves have more surface area to bounce and reflect off internally. Adding a filter will add another surface. The coatings are designed to help absorb these reflections.

The misting is commonly due to temperature variations. Getting out of the car (warm) and whacking the lens on the camera and setting up outside where there may be as much as 10 or more degrees of difference could cause this misting (the filter especially since it is a large surface area). Letting the camera and lens acclimatise for a few minutes. If I was in this situation, I would remove the filter and extend the lens barrel if using a zoom, or open up the focus to separate the lenses. This lets air circulate around them easier.

With your night shots, drop the ISO down to 400 and try a shutter speed of 16 times what you used for 3200 (or if you cannot wait the 5+ minutes, go to 800 ISO and go with 2.5 minutes). Night sky shots, I would avoid going beyond 800 ISO. Your battery will drain faster and the sensor may get warmer, which may create hotspots, but these will be easier to deal with in post processing than a higher ISO, and with stars, you may not even notice them (although most modern DSLRs will handle that without any issue). This is demonstrated in the silhouette of the trees. The longer shutter exposures too, will generate heat and could cause misting up, but I do not think that will affect things too much.

Looking at the first image, it looks as though there is a light source to the left, which suggests too long an exposure. I reckon you may have been able to get away with 800 ISO at 20 secs. Get a piece of dark card, and if you have a light source leaking into the shot, like that one, hold it to the side of the lens like a shade (but not in view obviously - you are trying to effectively create a shadow over the lens). With an ultra wide lens at 10mm, you will have to experiment a little to avoid it showing in the shot. Hoods have little or no effect.

Hoya used to do thin rimmed filters for these lenses, which will be beneficial. But a 10-20ish lens is one of the lenses I would not use a filter (because of additional flare and vignetting), the other is a dedicated macro lens either - you are adding an element that the rest of the elements were not designed to operate with. Remember, whilst they are designed as such, the primary reason most people have a UV filter on their lens is for protection. Incidentally, do not waste money getting a polarising filter for the ultra wide, especially if you plan to use for landscapes. I cannot remember the physics behind it, but if there is an expanse of sky in the shot and lets face it, an ultra wide is going to be used for mainly landscapes, it will lead to a distortion of the colours and their balance.

Thank you CLF,
I appreciate the advice.
I know the ISO should be as low as possible, but I also thought, from my own experience that the shutter speed should be kept to no more than around 20 seconds? If I go over that I end up with trails from the stars.

In the first image, the light source was the moon. It was a full moon and was creating so much light you could easily see where you were walking, even though we were in the middle of nowhere with absolutely no artificial light.

Can you explain your comment about what is demonstrated by the silhouette of the trees?

I have used Camlink filters for years and have never had a problem. I have a Tamron SP 10-24mm lens on my Nikon D5000.
Night photography can be hit and miss. But a decent tripod is an asset.

If the lens is misting up it's due to the camera/lens going from the warm to the cold. A drop in temperature will cause the misting and has nothing to do with the filter.

I have used every type of filter on the market. From the cheapest to the most expensive. Been taking photo's for over 60 years.