The GLD should be a very good lamp. Should be but I have not used one yet. More condenced
filament than that of a FEL it might be emulating in output.
So given a decent lamp and a
fixture that normally uses a G 9.5 lamp with a
LCL of 2.3/8", any lamp matching this will function in the
fixture assuming the wattage is within
rating which I don't doubt.
Given this, yes you would want a "
flat field" across the beam of light. The intent is to have a beam of light that's constant with little to no
drop off or bright spots across the beam. Otherwise for hot spot center with
drop off you would be wanting a
PC spotlight. Different intent and
fixture, though you can focus a
Leko to have a more hot spot to it's beam center. Is your
fixture focused for a hard
edge to it's beam of light?
Flat fields are what they are for the equipment in use - not all are perfect. On a
360Q for instance, you can for the most part get a
flat field but due to
reflector in-efficiency, the center will often be slightly darker than the main part and edges of the beam of light. That's what the internal lamp
reflector on a HPR lamp corrects for - the loss of light at the center of the beam where the lamp pops
thru a hole in the center of the
reflector. On the other
hand, dependant upon how good that
reflector is, on more later fixtures you should not notice as much this hole due to the concept of the
ellipsoidal reflector,
baffle and
lens train.
Pre-bench focus for this even field before installing the
gobo. One detail not mentioned is that sometimes even of a S-4, you just can't get a perfectly even
flat field of light. Sorry but it happens not all that infrequently that your beam of light just can't be cleaned up sufficiently. It's much based upon
fixture efficiency of light by way of design and individual fixtures or problems with them. Make sure that your lamp is fully seated and centered in the
reflector before bench focusing.
Could also have some individual
fixture problems. On a
Lycian 1290 follow spot for instance, if that spot gets a good bump there is a chance that the ellipse of the
reflector will warp and no longer provide a true ellipse. Much less in getting that bump, the
fixture itself can get out of square. Once something like this happens, there is no amount of
bench focus that will correct for this. Normally this out of square or ovaling of the
reflector will more show up more as a double
image or say instead of a hard sharp blue "hilation" all the way around the
edge of the beam, you will instead have almost a double ring if not half blue half amber when you otherwise have the most optimized beam possible for
bench focus. I thus doubt that this is your case but at times you might find say dots of bright spot across the
flat field that are also
lens/
reflector problems. One good way of bench focusing I have found is to first do the
bench focus but while looking at the beam of light, move it up and down on the wall. This movement of the beam will allow you to notice even slight problems with the beam more so than looking at a non-moving
image that your eyes will balance out for you so you can't otherwise notice them.
Ensure the curve of your lenses are facing each other, in their proper order of lenses given they are of different sizes and in their correct mounting position. If at some
point your
wash of light is not sufficient for a even beam of light after
bench focus, try another
fixture or two. Perhaps you have pulled initially a
fixture that just is not as good as another one. If even after that you can't get a perfect beam - and this should only be a
bench focus question, perhaps a different brand or type of lighting
fixture - one more optically refined will be necessary.
Anyway just some thoughts. Most of the
Leko companies will have supplemental information and advice on how to best
bench focus their gear. While what knobs are used to do this will be different, the same intent of what you are looking for will be in place.
Still all and all, given the proper hard
edge focus of the
fixture is not producting the hot spot - which I think would also
effect the rest of the
image quality, it's probably a
bench focus of the lamp issue.