Mixing lighting sources on HP5+ B&W Film

[thebdt]

Howdy all. I have a question about my lighting, and how it effects HP5+ B&W film (4x5 format, if that makes a difference).

I have been photographing flowers, using the modeling lights on two Calumet Genesis 400 strobes (the modeling lights are Halogen at around 3000 K, I believe, and are 150W each). Well, long story short, I broke one of the two modeling bulbs.

The replacement bulb is $25, and I either have to mail order it, or drive clear across to the other side of the county to get it.

I found a frosted "soft white" GE bulb, same wattage, at Home Depot; it screws in and appears to operate just fine. I tested it at half power (the Genesis modeling lights can be proportionally set) and it reads the same on my light meter as the remaining, functioning, original modeling lamp bulb.

My question is, is the difference in spectra between the original modeling bulb and the 'cool white' frosted household bulb enough to cause an appreciable difference on my B&W film (I'm using HP5+)? Will there be issues in how the film responds to a white flower, a green stalk (I am photographing mostly white flowers)? In short, will the spectral response from the "cool white" bulb be different enough from the original modeling bulb to produce uneven, poorly exposed negatives?

Or am I splitting too many hairs and worrying about something inconsequential?

Thanks for any input you can provide...

 

[Bosaiya]

You're going to have to give it a try and see for yourself. They will be different, but exactly how different and what that means to you is best left up to your own judgment. That you are using B&W and not color will minimize the differences to the point where I think you will not notice too much discrepency, but no one can tell you how you should feel about something so subjective.

My take: No appreciable difference.
Your take: Only you can decide.

 

[MetaGeorge]

If you like the new bulb, you have the option of buying a 2nd one at Hope Depot so they match.

 

[keithwms]

Mixed light isn't really much of an issue at all with the pan b&w films. The only thing to bear in mind is that if you filter, e.g. red or blue, then the filter factor will depend a bit on the colour spectrum of the illuminating light. But this is a relatively minor fudge factor that can be neglected unless you filter into deep red or UV.

The quality (fill, softness, contrast, specularity... if that's a word) and arrangement of the light are usually the most important things in b&w. Personally, I usually like my lights for b&w to be quite contrasty and almost gobo-ed in effect... to emphasize the shapes & textures with which b&w renderings excel. So I use tungsten lights, usually, with b&w.

 

[jeffreyg]

I don't often use lights (preferring available light) but have not noticed any problems with mixed light sources ( Ilford Delta 100, 400 & HP5). Frequently white flowers are not as white as we perceive them to be and some filtration helps such as a yellow or light orange and even a light green filter can make a difference. I would take frames with and without filters and perhaps meter through the filters ie off a gray card as opposed to accepting a published filter factor.

 

[Bosaiya]

In my experience the intensity of light varies between sources more than the "quality" of light. I do a lot of shots with multiple types of light (tungsten, halide, and LED) and I couldn't tell you which was which just by looking at the negative. You can add modifiers to any light source to either distinguish one from the others or too make them all more harmonious.

Don't sweat it too much, but do experiment and keep notes.

 

[thebdt]

Thanks for your input, all. I get the impression that it's not a big issue, but may indeed make a subtle difference. I'll note these negatives, and any differences (if any). I think, though, that going forward I'm going to buy some proper halogen bulbs and replace them into BOTH lights, same brand, for consistency. I found some ones in a compatible mount/wattage that are 1/3rd as much as the "official" Calumet ones...

 

[thebdt]

Well, I developed the film last night. There were two problems with the side of the flower lit by the "soft white" bulb:

1) Under-powered; what would normally be a blown out highlight edge along the stem was really just a very bright light, leaving texture and detail. I realize this isn't necessarily bad, but it was not what I was going for.

2) A weird, halo-like "glow" surrounded the flower where the "soft white" bulb light was hitting it. I was not going for this effect, either.

I went to Lowe's this morning, and found a halogen-based bulb that will fit the bill. It is a little more diffuse than the "original" bulb, but its color temperature (and I assume spectrum) are much closer to the OEM.

An interesting experiment...

 

[Harley]

Hi..
I believe the following the site would be the best source.

 

[sharris]

what gives?

Hi..
I believe the following the site would be the best source.

So what's with you and this link to the light and generator, Harley? Or am I missing something??

 

[Chazzy]

Why not just stock up on the correct bulb, so that a replacement is immediately available when needed?