Solar Filter for Super Zoom Lens?

[astrostu]

Being into astrophotography, I've photographed lots of objects in space, but I've never done the sun. I have a super zoom lens that's 500-1000 mm with a 72 mm aperture, but it also has a hood that threads on which has an aperture at the end of 77 mm.

I found a brand of solar filters for camera lenses online, and my question is: Would it be better to buy a 77 mm filter to put at the end of the hood, farther from the lens, or a 72 mm filter to put closer to the lens? Or, should I invest an additional $15 and get a step-down ring 77 -> 72 mm and get the 77 mm filter?

Thanks.

 

[j_mcquillen]

I'm not at all familiar with astrophotography, so I may be way off on this, but if I was taking 'regular' shots, I'd put my filters as close to the lens as possible... I can't see any advantage in putting the filter at the end of the lens hood - it may even lead to problems with vignetting etc.

 

[Mcfly50]

Nd 8 straight on lens and if need put a second one. High aperture low iso and you should have something pretty intresting

 

[astrostu]

Alright, thanks. Mainly the question I had was about glare, and having gotten a B in my college physics optics class, I couldn't figure out if there would be more glare if the filter were closer to or farther from the lens. So I'll go with the 72 mm and keep my fingers crossed for the results!

 

[benhasajeep]

It is recommended to have the filter on the end of the lens. As it will keep temperatures inside the lens down when shooting at the sun. Your lens is a big mangnifying glass (glasses) and the heat will rise inside the lens quite a bit. Also there will be less ghosting cause by the light bouncing around. I believe the lens you have does not have much coating so you will want to keep that down as well.

 

[SaSi]

There is certainly going to be flare. The zoom lens you describe sounds like a third party, budget lens. Even while they are called multicoated, they have the tendency to produce Great flare and low contrast.

I am not sure if you are going to overcome this, but no matter what lens I'd use, I'd use a polarizer filter. Shooting away from the sun, dictates circular polarizers. But straight, into the sun? Well, I don't know.

Another chance is that the ND filters are polarizers themselves.

 

[W.Smith]

ND filters cost a pretty penny. CD-R's are less than a buck apiece. You can use (an unburned, i.e. virginal) a CD-R as a solar filter to look at the sun through with the naked eye. Or even 2 CD's stacked if need be (it won't).

So I would experiment with a setup whereby a CD (or 2 stacked) is (are) stuck to the front of my lens with duct tape or some such. You could do that today, if you wanted.
Depending on the results you can always decide you need a regular ND filter. If you don't you'll have saved time and money.

 

[W.Smith]

There is certainly going to be flare. The zoom lens you describe sounds like a third party, budget lens. Even while they are called multicoated, they have the tendency to produce Great flare and low contrast.

The better the lens hood, the less the flare.

I am not sure if you are going to overcome this, but no matter what lens I'd use, I'd use a polarizer filter. Shooting away from the sun, dictates circular polarizers. But straight, into the sun? Well, I don't know.

Another chance is that the ND filters are polarizers themselves.

A polarizer won't have any polarizing effect when shooting straight into the sun. It'll only have some ND effect, but not nearly enough for looking straight into the sun. Don't use it for that! You'll damage your eyes and/or your camera's sensor!

 

[astrostu]

I really don't want to go with the CD approach for 2 main reasons. First, CDs don't offer a flat field that a real filter will, simply because they're not designed to be completely even across the entire disk and will usually have some sort of design on the front (my TDKs do, anyway). Second, with a near-80 mm aperture, CDs are not large enough to cover the entire opening of the camera without doubling them up, with the hole in one covered by the disk of another ... hence introducing even less of a flat field.

 

[W.Smith]

I really don't want to go with the CD approach for 2 main reasons. First, CDs don't offer a flat field that a real filter will, simply because they're not designed to be completely even across the entire disk and will usually have some sort of design on the front (my TDKs do, anyway).

An unburned, i.e. virginal CD-R is completely even, and especially has no design on the front since it is meant to be marked.

Second, with a near-80 mm aperture, CDs are not large enough to cover the entire opening of the camera without doubling them up, with the hole in one covered by the disk of another ... hence introducing even less of a flat field.

True, but if you're prepared to put up with the downside of CD-R's and be a little creative with duct tape it does provide a very cheap way to experiment with solar exposures.
While you're waiting for delivery of your stack of 77mm ND filters of course.