Oblique Masks

[rnabholz]

I have recently been experimenting with the use of Oblique masks.

The masks I was using were simply cut from a card stock. They were 32mm in diameter and had a handle that extends from the disk to aid in insertion and placement.

They did the job and I recommend that everyone consider making and trying something similar and give the technique a try.

After some use, the card stock began to fray, warp and crease making insertion and manipulation increasing difficult. I began to consider alternative, thinking that some type of plastic would be best.

In my cache of materials from various hobbies, I had some left over Kydex, a plastic sheet, black and opaque, somewhere between 1 and 2mm's thick, perfect for the task at hand.

I hear all of you thinking that you are pretty sure you don't have any Kydex laying around. But nearly any kind of flat plastic would serve, those inexpensive plastic report covers or small binders would be a good source. Check the recycling bin - there might be something in there that would serve. If all else fails, Amazon sells two 12x12" sheets for $10 - that would make a lot of masks.

You can cut the material with a sharp hobby knife, but it can be a struggle. Thinking about how to make it easier, I remembered I had a Dremel tool and the perfect bit for the purpose. It is called a "Side Cutting Bit" It will drill through the sheet, and then has cutting edges down the shaft that allow you to move the bit sideways and it will cut the material. That would be perfect for cutting the apertures in the disk.

Oblique Kit.jpg (119.42 KiB) Viewed 10239 times

I traced the outline of the mask on to the plastic using a pencil, and then drew the shape of the aperture I wanted to cut on the disk. I used a silver Sharpie to make it easy to see as I used the Dremel to cut the outline out.

Then, using the Dremel, simply removed the silver portion. Getting used to how the bit moved during the cut was a bit tricky, and you will see that there is some room for improvement in my abilities in that regard, but the mission was accomplished.

Oblique Cutter.jpg (103.66 KiB) Viewed 10239 times

As you can see, I did not cut the mask out of the stock until after I had cut the aperture - made handling the plastic during the cut much easier, and in the event that you make a mistake and ruin the mask, at least you had not wasted the time cutting it out. In this case, the cut was fine, and removing it from the stock was accomplished with some heavy duty scissors.

To give me the all of the available placement options, I needed three masks. One with the aperture at the top, one with it at the bottom and one with it on the side (that could be flipped to provide both right and left options).

Oblique Mask Set.jpg (154.44 KiB) Viewed 10239 times

Inserted in the condenser mask/filter slot, it looks like this

O Mask Straight.jpg (114.86 KiB) Viewed 10239 times

The slot provides about 60 degrees of rotation of the handle to fine tune the placement of the aperture. The narrow handle maximizes that range. Depending on the orientation of your subject in the field, you will likely find that seldom does the straight position give you that "perfect" effect, so having the ability to fine tune is helpful.

O Mask Offset.jpg (114.2 KiB) Viewed 10239 times

As you can see, my masks are not precisely made, but they do work just fine. They should be much more durable than the card stock.

Thanks for reading.

Rod

[JimT]

Good tutorial. Lots of thin black plastic food containers are also available that could work.

[billbillt]

Yep.. I like this.. Thanks for sharing..

BillT

[KurtM]

Hmmm, wonder if I just happen to have any "leftover Kydex" laying around the house...?

<rustles around in store room>

Dang! Down to just one little 4'x6' or 7' piece! (And I'm sure in the precise same thickness yours is.) (Wonder how many masks that could make?)

Moral of the story: You can always tell an old ATM, but you can't tell him much.

[rnabholz]

Good tutorial. Lots of thin black plastic food containers are also available that could work.

Thanks Jim

Yes absolutely, any plastic that is opaque and of appropriate thickness should work, like I mentioned, folks might have just the ticket laying in their recycling bin as we speak.

Thanks for the interest.

Rod

[rnabholz]

Yep.. I like this.. Thanks for sharing..

BillT

Thanks Bill.

[rnabholz]

Hmmm, wonder if I just happen to have any "leftover Kydex" laying around the house...?

<rustles around in store room>

Dang! Down to just one little 4'x6' or 7' piece! (And I'm sure in the precise same thickness yours is.) (Wonder how many masks that could make?)

Moral of the story: You can always tell an old ATM, but you can't tell him much.

I figured you might have a bit. As to how many masks it would make, well easily enough for a set for all forum members.

Everybody send your address to Kurt. ;^)

[DonSchaeffer]

Neat work. Let me ask, How would you describe the effects of these cut profiles? I found if I just block part of the light with a rectangular card, I can adjust the dark field quite a bit.

[rnabholz]

The effect is more a cousin to brightfield than darkfield, but I mention it because it offers another way to expand your scopes capabilities with almost no cost.

Oblique delivers images that show depth and relief which can offer some great insight into your subjects

Here are a couple of threads with some images.

viewtopic.php?p=42294#p42294

viewtopic.php?p=56994#p56994

[Greg Howald]

Hi Rod. You have a good idea. I did the same thing with a polarizing sheet. It was possible then to adjust the degree of polarization.
Greg

[rnabholz]

Thanks Greg.

I have some of that polarizing film laying around here somewhere, I will have to give that a try.

Thanks

Rod