Profile spot gobo focus problem

[Hougoumont]

Hello,

Forgive the following question - I'm very new to theatre lighting - my involvement is that I use such lights in a photographic studio. It's a tad unusual and I've had to learn an entire new set of jargon words - however I like the results so I'm sticking with my Quartzcolor and Berkey fresnels!

I have a LDR Suono 20/40 zoom profile that I've used so far reasonably successfully with steel breakup gobos. But... I have noticed that I cannot keep both the edges and centre in focus at the same time.. if the centre has a crisp projection then the edges do not, and vice versa. I can't believe that this is normal - so it either a) there's a trick I don't know about to get crisp projections across the frame, 2/ the LDR Suono is faulty in some way or 3/ it's just a crap lantern.. I have read people here aren't that keen on LDR.

Thanks in advance!

[david.elsbury]

You could try a donut? It’s a card (often made of CineFoil, or an aluminium pie dish..) cut to the same size as a cut of gel for the fixture, and with a hole cut in the middle. Place it in the gel slot. The smaller the hole the sharper the projected image but the dimmer the output.

 

Another option would be to get a profile with better optics. The Source 4 series have HD lens tubes which are optimised for gobo projection.

 

See also http://www.citytheatrical.com/Products/donuts?dept=36ad06a1-84a1-43c4-a654-cc6e4ee51140

Edited January 29, 2020 by david.elsbury

[indyld]

It's pretty normal particularly if you have a fairly standard zoom spot with angles such as a 20/44 that is set on the widest setting. A wide beam spread and a short throw distance have a greater difference between the throws at the the centre and the edges. In that situation the focus is always a compromise.

[livewire4989]

Hello,

Forgive the following question - I'm very new to theatre lighting - my involvement is that I use such lights in a photographic studio. It's a tad unusual and I've had to learn an entire new set of jargon words - however I like the results so I'm sticking with my Quartzcolor and Berkey fresnels!

I have a LDR Suono 20/40 zoom profile that I've used so far reasonably successfully with steel breakup gobos. But... I have noticed that I cannot keep both the edges and centre in focus at the same time.. if the centre has a crisp projection then the edges do not, and vice versa. I can't believe that this is normal - so it either a) there's a trick I don't know about to get crisp projections across the frame, 2/ the LDR Suono is faulty in some way or 3/ it's just a crap lantern.. I have read people here aren't that keen on LDR.

Thanks in advance!

 

Hi,

 

Have you owned the lantern for long or is it something you have recently purchased new / second hand?

 

Kind regards,

 

Dennis

[Hougoumont]

Hello,

Forgive the following question - I'm very new to theatre lighting - my involvement is that I use such lights in a photographic studio. It's a tad unusual and I've had to learn an entire new set of jargon words - however I like the results so I'm sticking with my Quartzcolor and Berkey fresnels!

I have a LDR Suono 20/40 zoom profile that I've used so far reasonably successfully with steel breakup gobos. But... I have noticed that I cannot keep both the edges and centre in focus at the same time.. if the centre has a crisp projection then the edges do not, and vice versa. I can't believe that this is normal - so it either a) there's a trick I don't know about to get crisp projections across the frame, 2/ the LDR Suono is faulty in some way or 3/ it's just a crap lantern.. I have read people here aren't that keen on LDR.

Thanks in advance!

 

Hi,

 

Have you owned the lantern for long or is it something you have recently purchased new / second hand?

 

Kind regards,

 

Dennis

 

Hi Dennis,

I bought it maybe 3-4 years ago from a popular auction site (without shutters as I didn't know what I was doing!) but only used it as a spot very occasionally. It's only recently I've been experimenting with gobos as photographic backdrops - just using breakups and because I typically use a wide aperture (say f/4) when shooting portraits the projection is out of focus in any case. It works well. Now I'm wanting a sharp projection (specifically a night city scape) and will therefore close down the camera lens to f/8 or f/16 - that's where my plan is falling apart.

Bob

 

It's pretty normal particularly if you have a fairly standard zoom spot with angles such as a 20/44 that is set on the widest setting. A wide beam spread and a short throw distance have a greater difference between the throws at the the centre and the edges. In that situation the focus is always a compromise.

 

Thanks Rob,

This is what I feared :(

 

I only have a throw distance of 5 maybe 6 metres available (in my studio anyway) and wanting a projection diameter of around 3 to 4 metres. I am asking too much?

I had thought of a Selecon SPX profile (there are some going cheap on that auction site) based on a) I think the optics are better than the LDR and b) according to the seller the standard bulb is brighter than a Source 4 and apparently with a 800w bulb outperforms a Juliat 2k - at which point I could maybe use a donut. The LDR is not bright enough anyway without a donut. Alternatively I give up on the profile and try various flash gobo projectors that are now seen in photography - although I'm not convinced by what I've seen of such tools so far. ...or I go back to Photoshop, slide in a high res image of a gobo as a background. Easily done - although I'm trying to stay away from such trickery as much as possible and do (almost) everything in camera. Bob

 

You could try a donut? It's a card (often made of CineFoil, or an aluminium pie dish..) cut to the same size as a cut of gel for the fixture, and with a hole cut in the middle. Place it in the gel slot. The smaller the hole the sharper the projected image but the dimmer the output.

 

Another option would be to get a profile with better optics. The Source 4 series have HD lens tubes which are optimised for gobo projection.

 

See also http://www.citytheat...54-cc6e4ee51140

 

Thanks David,

I'll try that - it makes sense as it'll do the same job as the iris in a camera lens. I suspect however that it really will be too dim - as the LDR on 650w (the max) is not enough anyway for my purposes. A more powerful profile with a donut might be an option.Bob

 

[paulears]

The description plays a little bit with the optics description. Strand had some profiles that used a series of lenses to make the gobo projection much sharper, and they called them condensers, as a different optical lens combination to their own 'normal' profiles. They used smaller gobo's too, because the beam diameter at the focal point was smaller. I think your's just used the normal pair of Plano-convex or convex lenses for the zoom. so the actual focal plane is quite blurry from centre to periphery. Can you adjust the throw distance, or is it only wide enough when the lantern is as far away as you can get it, on the widest zoom setting? Sometimes changing the distance can make a difference. Also - are you sure you have the correct size gobo? It says M and D, so if you have the D size, a swap to M could help and let you either zoom in, or move it physically closer.

[indyld]

The beam width at 40 degrees on a 5m throw is about 3.6m so it seems like you are working at the difficult end of the zoom. In a studio environment, I'd also imagine that you are already stretching the few lumens that dribble out of the end of 650w tungsten spot spraying as wide as it can manage over 5m, and as you suggest a doughnut will likely result in an extra disappointing output compared to the rest of lighting in the setup. We can get away with this in dark theatres with low light levels and high contrasts. I assume you are already avoiding having your main light spilling onto the background?

 

As Paul suggests, check that you are using the largest gobo size the fixture was designed for. Just in case you are cutting light output or making the spot zoom wider than it needs to.

Edited January 29, 2020 by indyld

[Hougoumont]

The description plays a little bit with the optics description. Strand had some profiles that used a series of lenses to make the gobo projection much sharper, and they called them condensers, as a different optical lens combination to their own 'normal' profiles. They used smaller gobo's too, because the beam diameter at the focal point was smaller. I think your's just used the normal pair of Plano-convex or convex lenses for the zoom. so the actual focal plane is quite blurry from centre to periphery. Can you adjust the throw distance, or is it only wide enough when the lantern is as far away as you can get it, on the widest zoom setting? Sometimes changing the distance can make a difference. Also - are you sure you have the correct size gobo? It says M and D, so if you have the D size, a swap to M could help and let you either zoom in, or move it physically closer.

 

It's got three lenses - two movable (plano-convex as far as I can judge) and one fixed in front of the bulb. I've been able to take the throw to around 8m (by going outside!) simply to test - at that distance the focus across the plane improves - but still not good. I'm using M sized gobos already.

 

The beam width at 40 degrees on a 5m throw is about 3.6m so it seems like you are working at the difficult end of the zoom. In a studio environment, I'd also imagine that you are already stretching the few lumens that dribble out of the end of 650w tungsten spot spraying as wide as it can manage over 5m, and as you suggest a doughnut will likely result in an extra disappointing output compared to the rest of lighting in the setup. We can get away with this in dark theatres with low light levels and high contrasts. I assume you are already avoiding having your main light spilling onto the background?

 

As Paul suggests, check that you are using the largest gobo size the fixture was designed for. Just in case you are cutting light output or making the spot zoom wider than it needs to.

You're right - dribbling is the word! I'm using, normally, one key light and one hair light (sometimes a kicker as well) and all have the barn doors closed right down - the key is slightly wider as I'm lighting 'down the nose' and want a column of light just to illuminate the subject and no wider. If I need a light on a prop (for example) I'll light that separately and again control the spill.

One thing I've not tried is covering the white walls (that might create bounce onto the backdrop) or flagging - a kind theatre installer let me have the surplus heavy-weight wool drapes(?) that are used on stage wings (not learnt that word yet) and I may try that. It's incredible stuff - absorbs light like black hole and far better than anything supplied for normal photographic use.

Or... I may just buy this Selecon SPX - if I can get one stop more light on the backdrop I'll be happy (ok, that's doubling light.. I'll be ecstatic... even 1/2 stop would help) - and perhaps the gobo projection will be better. I'll have to replace all the gobos going from M to B though...

 

[livewire4989]

Hi Bob,

 

As you have had the lantern for a number of years it would be worth making sure all of the lenses are sparkling clean as dirt / grease build up on these will cause the image outputted to be less sharply focused. Also if the gobo fitted is made of steel these can warp with use; if the gobo is not sitting flat in the gobo holder you will get varying focal points when attempting to sharply focus. Hope this helps.

 

If you need anything else just let me know.

 

Kind regards,

 

Dennis

[Hougoumont]

Hi Bob,

 

As you have had the lantern for a number of years it would be worth making sure all of the lenses are sparkling clean as dirt / grease build up on these will cause the image outputted to be less sharply focused. Also if the gobo fitted is made of steel these can warp with use; if the gobo is not sitting flat in the gobo holder you will get varying focal points when attempting to sharply focus. Hope this helps.

 

If you need anything else just let me know.

 

Kind regards,

 

Dennis

 

Thanks Dennis,

I'll give the lenses a clean - I assume camera wipes are ok? I'm getting chromatic aberration at the edges and I guess that could be grease/dirt? The latest gobo is brand new and sitting flat - or as flat as my limited experience tells me.

 

[alistermorton]

We use a weak solution of washing up liquid and water to get the first load of muck off the lenses, then a rinse then a final wipe with alcohol, then polish with a lint free cloth. It does make a noticable difference to the light output.

 

Colour fringing at the edges isn't unheard of with profiles, especially older designs. As the image defocusses you get blue or brown colouration usually. Newer "high definition" lens tube designs are better at controlling this.

[RumbleO]

Just a simple thought... ... Would curving the backdrop, so the edges and the centre are more equidistant from the lantern, improve focus across the backdrop? :unsure: