[Nass]

Hello,

I've had some lamentable results stacking cokin filters on my K-7 (pink magenta cast) and I'm looking for a strong ND solution. There seem to be various choices:

1. Pro ND10 filter
2. Vari-ND
3. Stacked polarisers
4. Welder's glass
5. Stacked Cokin & IR

From what I gather Pentax cameras let through more infra red than other brands, or somesuch thing, hence the cast. Could I possibly ask those of you who do successfully take long exposure during the day (ie 1-5 minutes) what combo works with you?

Many thanks

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Last edited by Nass; 03-12-2010 at 01:39 PM. Reason: replaced ND 10 with strong ND

[ambienthousewife]

I have tried a few of your solutions. Vari-ND is based on stacked polarisers, but I have not used one. I have stacked various polarisers that I had lying about, some £10 from ebay and some old linear versions. I have tried all the combinations but have not had good results. Magenta casts and cross shaped effects, where the cross is dark magenta and the corners outside the cross are lighter. Welders glass is great and cheap at £4, but it is VERY dark (the one I have is about 20 stops) and green. You can correct most of the colour cast, but you have to ensure that it is clean and scratch free or you will get flare effects around defects. Also, light leaking behind any of these is an absolute no-no (so makes cokin filters a bit of a trial to control). Light leaking back through the viewfinder is a real issue as well (with my Kx and K100,) so block the viewfinder. Cokin & IR is fine, but it will be IR, so not really realistic. I had a good example of the Citiwide ND400 which I gave away. It had a magenta tint as well, but was interesting to use and probably 15 stops rather than the rated 9. Sadly the new versions of that filter were faulty (creating the same magenta cross as bad crossed polarisers, so you can guess how they made it. It is no longer on sale, but if they can fix the problem I would buy another, they were only £13). So all those will cause you problems, and you are left with the expensive solutions. I have a B+W ND110. The 58mm was only £30 I think, the 77mm was closer to £80, but they do actually work well for landscape. There is a slight pinkinsh cast, but it is easily correctbale. I feel that I wasted a few quid on cheap attempts, but do not regret getting either of the B+W ND110s I have.

This is one with the welding filter (this was just to try it out, I would have preferred some moving clouds or something to blur)

There are some with the B+W here Picasa Web Albums - David - Beach Neutral...

Moved to lens forum.

[Nass]

Thanks David, that's very useful. I have 6(!) polarisers in my bag so I'll probable spend the weekend trying this out. Many magenta coloured images later I'm sure that I'll conclude exactly the same as you

Seems to me for this sort of stuff a very wide mm ND110 with stepdowns would probably be the most lasting solution?

Also, one thing I'm slightly unclear about and I alluded to, I've seen a lot of claims on various sites that Pentax dslrs are especially prone to this because they let in more IR than other brands. Are there any Pentax dslr/other brand dslr experts in the house that might be able to cast some light on this? can this feature of Pentax dslrs be used to our advantage? Should I discuss this in a seperate thread in the pentax dslr subforum?

[MattGunn]

Have you come across / considered Baader solar film? (Details here: Baader Planetarium - tech information about Baaders AstroSolar™)
It is designed for photographing the sun and so should provide a good attenuation across the spectrum. The density is only 5 but stacking it should not cause any problems. It is pretty cheep and you can make up any size filter you desire.

[georgweb]

I'd say you will get cheaper with those filters the more patient you are. All those abandoned film equipments have tons of filters with them and it is likely you can get some nice ones (even the older B+W) for about the tenth of the shop-price.

I ended up with two Lytkarino ND4x which I can stack if needed. You gotta make sure to have very good flare protection (hood + your hand +...). Shoot raw to get rid of any color cast. I have used cheap ND8x glass filters too and I guess they do the job as long as it it's glass.

My max. ND8x is enough for blazing sunlight and f/1.2 at 1/4000s. to retain shallow DOF if needed. For long exposures the ND8x is good for me too. That'll be in the 3-30 sec. department and I am wondering what you want to do with a 1-5 minute exposure. Also, remember to not walk around the tripod or have cars or trains rush by or any other cause of vibration - because all that will give you a more blurry pic. Finally bring some spare batteries .-)


Jupiter 85/2 @f/16 on K100D + ND8x 6sec. exposure

[Nass]

Have you come across / considered Baader solar film? (Details here: Baader Planetarium - tech information about Baaders AstroSolar™)
It is designed for photographing the sun and so should provide a good attenuation across the spectrum. The density is only 5 but stacking it should not cause any problems. It is pretty cheep and you can make up any size filter you desire.

Super idea, I wondered about the optical qualities of this though. I'd thought earlier this afternoon that a good solution might be this sort of stuff, cut in a circle, sandwiched between two cheap clear UV filters (actually I was looking at the Lee gels with this but I suspect that's more for lighting than a lens).

[little laker]

From what I gather Pentax cameras let through more infra red than other brands, or somesuch thing, hence the cast.

Just a thought, but why not use Custom White Balance? That should eliminate the color cast

[Nass]

George, excellent advice as always - there's a lovely old bits and pieces store about an hour away and I'm tempted to go and rummage there.

I've seen some clever stuff on Flickr done with long exposures, and being a "wannabe" I'd like to have a play and try that too!

• Mimic on Flickr - Photo Sharing!
• K on the Horizon on Flickr - Photo Sharing!
• Fence on Flickr - Photo Sharing!
• Construction of the Unfinished | HDR (Explored No.1) on Flickr - Photo Sharing!
• Mupe Rocks! on Flickr - Photo Sharing!

I must admit I'm still unclear about the Pentax aspect of this equation though, since the concensus appears to be that Pentax dslrs do have a different behaviour to such things as 2 stacked polarisers or stacked ND grads (the cheap cokin type) because they let in more infra red:

• Do Not Buy A Pentax ist DL if you want to use ND filter - Photo.net Pentax Forum "Do Not Buy A Pentax ist DL if you want to use ND filter"
• http://www.flickr.com/groups/canoneo...7607867670991/ "CCD sensors are more sensible to IR than CMOS. That's one of the reasons why the Pentax is a good camera for IR photography."

Perhaps this is hogwash or perhaps there is something to it or perhaps it's just some of the sensors (ie does this pertain to K-7, mine)? And would that then logically mean some Pentax dslr bodies need overcompensation?

*thinks of Falconeye who has the most amazing stats at his disposal*

I'd say you will get cheaper with those filters the more patient you are. All those abandoned film equipments have tons of filters with them and it is likely you can get some nice ones (even the older B+W) for about the tenth of the shop-price.

I ended up with two Lytkarino ND4x which I can stack if needed. You gotta make sure to have very good flare protection (hood + your hand +...). Shoot raw to get rid of any color cast. I have used cheap ND8x glass filters too and I guess they do the job as long as it it's glass.

My max. ND8x is enough for blazing sunlight and f/1.2 at 1/4000s. to retain shallow DOF if needed. For long exposures the ND8x is good for me too. That'll be in the 3-30 sec. department and I am wondering what you want to do with a 1-5 minute exposure. Also, remember to not walk around the tripod or have cars or trains rush by or any other cause of vibration - because all that will give you a more blurry pic. Finally bring some spare batteries .-)


Jupiter 85/2 @f/16 on K100D + ND8x 6sec. exposure

[MattGunn]

Super idea, I wondered about the optical qualities of this though. I'd thought earlier this afternoon that a good solution might be this sort of stuff, cut in a circle, sandwiched between two cheap clear UV filters (actually I was looking at the Lee gels with this but I suspect that's more for lighting than a lens).

If the claims on their website are true then this stuff should provide the same optical quality as top of the range glass filters. It is not supposed to be pulled tight, just left slightly crumpled - counterintuative but it works. As it is so thin there is not much there to contribute aberations and having it not flat pretty much eliminates ghosting etc. We have some at work on a Meade telescope for observing sun spots and it workes great.

[ambienthousewife]

Also, one thing I'm slightly unclear about and I alluded to, I've seen a lot of claims on various sites that Pentax dslrs are especially prone to this because they let in more IR than other brands.

God I hate it when the moderators move things to really obscure locations! How on earth is this lenses?

I have seen some awful shots of infrared contamination with other cameras, I think it is more a factor of the filter than the camera. Hitech are supposed to be pretty prone to IR leakage. Remember that polarising filters are usually transparent to infrared, which is why when the visible light is blocked as you cross them, they still transmit a lot of IR, causing the magenta tone. I think blaming pentax is a cop out for some filter manufacturers, although it is true that it is pretty easy to use an unmodified pentax and get reasonably good results with just an infrared filter. I was going to buy a sheet of that solar film, especially as I was trying to work out a filter for the fisheye lens. I would be interested to see some results using it.

[Nass]

Likewise, that film looks interesting. I mailed Falconeye and he recommended that film too, which is a good shout I think. It comes in 2 grades and it strikes me that it might be a good budget solution to cover all my lenses, especially the sigma 8-16 which I'm resigned to, if I get some large UVs, have that stuff in the middle and use stepdowns.

I tried fiddling with as many combinations (linear/circ) and sequences (reversed/normal) but none of them were neutral or even, sadly. When/if I ever get time I'll probably also pop along to Mr Cad's (just down the road from both of us) to see if there's anything there along ND4 lines which stack that I can pick up along the lines of georgweb's suggestion as well.

[ambienthousewife]

Little Laker - it got buried back there, but good tip about custom white balance. You need a fair amount of light coming in for the camera to set a custom balance, the 20 stop welding filter is nearly impossible as it is too dark for a reading, but it helps a lot with the 'standard' dark filters.

I'll probably also pop along to Mr Cad's (just down the road from both of us) to see if there's anything there along ND4 lines

Yes, they would be worth a shot, I think I went there about 20 years ago and it was a goldmine. Need to beat you by the sounds of it! They seem to have a suitable range from a quick search on their site. I was in Arundel and the photo guy there has stacks of filters as well, I did not look, but I think most were smaller UV etc.

[Nass]

Follow-up, I've purchased some of that film from Germany and it should arrive today or tomorrow. I'll make my own filter out of it and post the results back here when I've got something worth looking at

[Ben_Edict]

Super idea, I wondered about the optical qualities of this though. I'd thought earlier this afternoon that a good solution might be this sort of stuff, cut in a circle, sandwiched between two cheap clear UV filters (actually I was looking at the Lee gels with this but I suspect that's more for lighting than a lens).

Baader's solar filter foil is the best quality you can get. It is great for visual observation at high magnifications and photography is much less demanding. The only problem may be mounting it to your lenses. You cannot simply put it into your filter holder (Cokin and other have gel holders for their filter systems), because the foil is highly reflective. You need to put it really light tight into the fornt of your lens. You could simply type it, as some crinkles won't degrade the IQ!

I have been using that foil for years on my telescopes. They are available in two different densities, so the choice is yours.

Ben