Fishrock Dives SRP filter on GoPro Dive housing

[toozler]

I understand the thickness correlation, but my curiosity is more on the tint vs f-stop, than the thickness vs f-stop.

Correct me if I'm wrong, but if a filter is designed to absorb a large portion of the blue and green wavelengths it is also proportionally reducing the overall amount of light captured by the sensor, thus forcing the camera to increase it's sensitivity to light and introducing more noise. It will have a greater effect on re-introducing the reds and oranges, but at the expense of more noise.

The choice of material by these manufacturers may be a decision due to the desired physical properties (i.e. stiffness, resistance to scratches) rather than its optical properties. There are materials much thinner than those used on these external filters that can filter out nearly 100% of the blue and green wave lenghts (but reducing light transmission to nearly 15%).

I don't own any of these Marty tested, but based on the pictures, I notice a lot of noise on all, some more than others, and understand the trade-off: more reds, more noise; less reds, less noise. I would be more inclined for a less "aggressive" filter to bring back just enough reds that can be later improved in post-editing. Noise can't be removed, but masked by increasing contrast, which affects everything else.

 

[Interceptor121]

toozler the reason why you see more noise is that if you look at exposure there are three variables: shutter speed, aperture and ISO
Aperture for the gopro is fixed, shutter speed is also kinda fixed so the final outcome is
Less light from absorption of the filter --> higher ISO to compensate --> more noise
If you assume a filter to take 1 f-stop this means that at depths such those Marty took shots there is not much light
The filter will take the ISO from 400->800 or 800->1600 at some point there will be just a lot of noise
This is the point I was making to Marty yes it looks less green with a filter but it does have more noise at the end do you want more colour and more grains or cleaner greener picture? A matter of choice, I prefer a cleaner greener picture and convert to BW

 

[toozler]

We are on the same boat here.

 

[Marty Cerven]

toozler the reason why you see more noise is that if you look at exposure there are three variables: shutter speed, aperture and ISO
Aperture for the gopro is fixed, shutter speed is also kinda fixed so the final outcome is
Less light from absorption of the filter --> higher ISO to compensate --> more noise
If you assume a filter to take 1 f-stop this means that at depths such those Marty took shots there is not much light
The filter will take the ISO from 400->800 or 800->1600 at some point there will be just a lot of noise
This is the point I was making to Marty yes it looks less green with a filter but it does have more noise at the end do you want more colour and more grains or cleaner greener picture? A matter of choice, I prefer a cleaner greener picture and convert to BW

Thats the choice we all need to make but only at the deep end limit, in good light at depths where the filter works well id take a little grain and more colours anyday over the colourless video. At depths and light levels where the filters are struggling you can make that choice but many times the gopro with no filter not only goes green but ends up with what looks like a green overexposure type effect. This blows all highlights into a single shade of green and id rather take grainy filter footage over this which i think is completly unusable. It kind of shows thought that once you dont have enough light for a filter with a gopro you really dont have enough to get decent footage even without a filter and only lights will help at that point.

I deliberatly did most of the diving here at around the filters depth limits, not really to show how good the filters work but more what their limits are. Had I had better conditions the results would have been a little different but in this sort of light your best sticking to the urpro recomendation of 25m total distance.

The gopro is not a great low light camera so diving beyond 20m with filters for decent results you need very good vis and light. But the difference the filters make with favourable depths and conditions is why I never dive with a clear lens anymore, the clear lens loses all colours so early. The main reason my 3d dive housing is gathering dust is because once I started using filters the unfiltered footage leaves me much more disappointed now.

I was hoping to get better footage at he the 20-25m level and all the shallower stuff but unfortunatly the weather wasnt playing nice enough and for best filtered footage at that level you do need a bit of luck condition wise. This ended up more as a filter limit test then anything else due to the poor conditions.

 

[Interceptor121]

I think the GoPro is not bad in low light if you look at the specs 0.84 lux/sec however due to the tiny sensor there is plenty of noise
Low Light Performance - GoPro HD Hero2 Camcorder Review
However with a filter should have good color rendering
I guess the GoPro gives his best around 15-18 meters or 50-60 feet that by coincidence is the working range of the magic filter!

 

[Marty Cerven]

I think the magic isnt quite best at that range more like 6-12m and it starts to lose colour from that point pretty quick compared to the other 2. In poorer light it didnt correct colour better then the other 2 I used much past those depths, and ended up many times equal to no filter. But by working best to shallower levels even though its the thickest it still is the lightest allowing more light so slightly less noise at deeper levels in low light, when beyond all the filters working range.

In better light though from all my use with urpro filters with gopros and also going by others peoples tests with the new filters the urpro's do quite well at 25m still, but my conditions cut the effective depth to more like 15-20m and magic were best 5-10m shallower on average in terms of retaining colours at depth.

 

[Interceptor121]

5-10 not godo enough
Alex mustard is a clever guy I think the filter is designed for conditions better than those you have there
Probably in Egypt or Caribbean it will be good at 15-18 meters

 

[Marty Cerven]

Maybe you misunderstood what I tried to say, I think the magic filters work best about 5 to 10m shallower then the urpro given the same conditions. In the conditions I had this was not much beyond 12m but also the urpro was best not much beyond 20m in these same conditions.

 

[Interceptor121]

Ah ok. So you are saying at shallower depths magic seems best and then URPRO takes over
The physics would explain that as the magic is thicker so absorbs more light and is more red than orange so it should give its best in the 5-10 range according to the optics theory
The URPRO being more orange and thinner should kick in at best around the 10 meter mark
Both filters should only be used after the first 4.5 meters of 15 feet
If I understand what you are saying that would make sense

 

[Marty Cerven]

The magic and urpro filters do have a slightly different filter colour so they do will work in a different way, but I think its a bit more like comparing the shallow water cyan and regular cyan filters by URPro. These to the eye look nearly identical the only difference you will notice is that the shallow water version is fractionally more transparent if you look at it very closely. Sitting both filters on a camera without looking at the filter ring that says cy or swcy I could easily mistake the 2 filters. This means the swcy allows more light and even though they are both a near identical filter colour as far as I can tell, also exact same thickness and in the case of the 2 I have, both are glass yet they perform very differently underwater at different depth levels.

So when comparing the Magic filter and URPro cyan in this case, even though the material thickness is fairly different between the 2. The magic filter works a bit more like the shallow water cyan filter. From what I can tell its kind of between the 2 working deeper then the swcy but not as deep as the regular cyan by urpro if that makes sense. The URPro swcy is best at 5m or shallower and then it begins to lose colour but at the shallower levels it lets in more light so it does a much better job then the regular cyan filter does at these levels.

I have still used a regular urpro cyan at the shallow levels and with a basic wb adjustment results can be pretty good but the swcy will still always do a little better as it let in more light so therefore less noise and more detail in the final image. This swcy filter though much beyond 5-8m will pretty much not correct colour any more and will act almost as a clear lens, it will reduce a little light still so performance wise the clear would still be slightly better beyond its working depth.

Now if I haven't lost you yet using this same concept even though this time we are comparing 2 different filter colours and very different filter constructions and thicknesses, one has been designed for a deeper optimum depth then the other so the magic will do a little better in the shallow end 5-10m but beyond 15m does lose most of its colour correcting abilities. Backscatter has mentioned elsewhere that their filter is best at 15m or less and I have noticed it pretty much match these specs. The urpro cyan will hold up close to the rated 25m in good light but due to filtering out a bit more light in the shallower end will be beaten by the magic filter slightly at those levels, but then you have variables in filter construction that may have other effects too. These depths I mean total distance so depth plus distance to subject and conditions can effect this + or - 5m in poor or great conditions quite easily.

The difference between the magic and urpro at the shallow end arent quite as drastic as they are between a CY and swCY by URPro but still noticeable, but both not much beyond the rated depths do drop off most colour correction pretty quickly.

Then comparing the URPro and oculus which seems to have copied the colour of the filter pretty closely to the urpro cyan filter but also filters a out bit more light overall. This can also be due to the material used which may not be as optically efficient as both the magic and urpro filter material and so though it does hold up quite well to it gives a few odd results in terms of colours which look less natural. At the shallower end also the oculus has the worst results of the lot being very orange at under 5m but then closer to the urpro from there on maybe working a couple meters deeper but tends to have a bit more of a colour shift towards orange.

When looking at the shallow end I still prefer a filter at 2-5m even if the original result may be a little too red, this can be easily corrected in post with the slate and wb adjustments giving colours that will match up better to the other filtered footage within the filters working depths. No filter starts losing most colour not much beyond 2m and so at 5m will be very colourless compared to a filtered shot at 5-15m.

I dont know how much effect the thickness has as you can have a very thick piece of glass or thin glass not have a huge difference on the amount of light getting through, but change the amount of tint on either one and you can easily make the thicker one allow more light then the thinner pieces so its not really the determining factor I think.