Explore Scientific 2" UHC filter

[Mrbloke]

There's still not too much info out there about these filters, so I thought I'd start off a thread that can further define this elusive item.  I bought this filter on the back of all the other explore scientific products that I have purchased being, in my mind, excellent value for money.

Firstly, the filter (much like all ES products) is delivered in a beautiful presentation case.  The box is adorned with star maps designed by Wil Tirion and the filter itself sits neatly in its own plastic case within.  I was a little surprised to find that the outer box is made of MDF so is wooden, rather than cardboard.  It also contains hidden magnets in the lid and base that securely 'click' the lid shut, which is a nice touch.  Each filter comes with its own serial number and associated test sheet.  The type of filter and the serial number are printed around the edge of the filter along with the maker.

The filter itself feels solidly made with a uniform purple or green tint as you change the angle you look through.  It screws into the 2" eyepieces that I have easily, but although the complete unit feels smooth and equal diameter to the touch, I do have to make sure the compression rings on the draw tube are completely undone as it does seem to stick a little bit more than the eyepiece alone - not sure how normal this is as this is the first filter I have had.

Filter batch comparison

Firstly, a shameless plagiarism of others' work on this forum.  Apologies in advance for your test sheets!  On the left is one from the ES website (tweaked by BigSumorian), the middle bingevader and on the right, mine.  Although broadly comparable in shape, it would appear that my later filter has the same profile, but transposed approximately -10nm throughout.  I do not have the tiny pre-peak seen at 450nm, but have got a noticable dip mid-peak at 470nm.  The transition at 620-640nm is slightly faster over the previous two filters.

Whether these variances are due to process variability, process improvement, test machine (they are different - but should be equivalent) or operator we will never know.

Filter comparison

I have overlaid the Explore Scientific UHC onto this filter comparison here as a narrow black line.  The first thing that stands out is that this filter is much wider than the comparable bunch, starting way before any of the others.  The cut-off at the other end of the main bandpass of interest appears to be par for the course.  I've had a closer look at the 500.7nm OIII line from the original graph I have and it appears to -just- capture it.  Transmission is amongst the best, surpassed only by the Lumicon.

Outside the main peak, there appears to be zero transmission below 430nm.  The peak at 640-700nm has the highest transmission of all the filters and forms a plateau, which is different to how the others are performing at this range.

Performance

Well, this part is going to be a work in progress.  Sorry to disappoint.  I want to get more of a season in (especially M42) and a few dark sites before I commit to anything.  Also I have nothing to compare it to, but am happy to meet up for a side by side.  I will say that it has produced pleasing views so far, and at nearly 1/3rd of the price of the equivalent Lumicon, I don't think my light polluted skies could justify the cost of the upgrade!

[John]

Very interesting, so far, George

The big test is the performance of course.

Ideally you would try it out side by side with competitors, in the same scope on the same objects, same eyepieces, under the same conditions, as thats the only way to find out how these things compare in my experience.

I understand that the above is difficult to arrange though and I'm sure that we will all be interested in what you think of the ES filter. At least you can make "with" and "without" filter comparisons on suitable test objects

[alan potts]

Nice reoprt, I look forward to hearing more, these are fairly new to the market I think, I wonder who makes the glass as I am sure that it will be in other named filters, I have never seen anything that suggests that Lumicon and Astronomik's make for others, it must be a fairly specialised prcess.

Alan

[bingevader]

No apology necessary on my behalf!

I'll dig out my reports so far and add them too if you don't mind.

Unfortunately, life and the weather are interfering with my observing lately, but I'll do my best.

Yep, a side by side report with other filters for comparison would be lovely.