Bellows versus Helicoid

[woodrim]

I'm wondering how effective a bellows might be as a method of adapting projector lenses instead of using helicoids to focus. Anyone?

[BurstMox]

I believe bellow are more convenient for long focal projector lens as it has long range of focus.
At opposite, helicoide are better for projector lenses like 75mm since you don't need a lot of range in focus in order to go from infinity to close focus.

[cooltouch]

I'm inclined to agree with Pierre. This reminds me of the very long R telephotos that Canon produced in the 1960s. The longest was 1200mm. It didn't have a focusing helical, rather it had a bellows at the rear.

[luisalegria]

Bellows normally are too thick for infinity with lenses under 100mm, and many are too thick even for that.

Bellows are much cheaper than helicals though.

You can find rather short bellows. Look for the folding Kopil brand.
There are many available in M42 particularly.
These may require some lubrication/loosening up.

A cheap vintage helical thats a bit scarce is the Spiratone/Accura variable extension ring, made in the 1960s-70s. It takes some clever searching on ebay. They are good for 75-90mm depending on your ability to mount lenses deep in the device. I use one for a 75mm Petzval.

[dickb]

In addition to the previous considerations, be aware that bellows can be a little more cumbersome to use. Depending on the sturdiness of the bellows and the weight of the lens you may or may not need to lock the movement of the bellows every time you adjust its length. YMMV.

[woodrim]

Thanks to all for the advice. My initial thought was to save having to purchase separate extensions for each lens by applying a simple and cheap adapter (M42 or whatever) to the rear of each lens, then using the bellows for the needed extension and focusing. I suppose depending on which bellows, that I can get caught with too long a minimum extension. Perhaps I can accomplish the same thing by using a helicoid of sufficient range for multiple type lenses. Right now the two lenses I most want to use are the Diaplan 2.8/100 and a Trioplan 3.5/75 from a folding camera. I'm expecting good things from both, although the 75mm most likely will not have the same quality bubble bokeh as the Diaplan.

[calvin83]

You can use a combo of bellow/helicoid/tubes.

[DConvert]