Redrock Macro adapter on SurplusShed

[Thagomizer]

Until I do more shooting out in the field, rather than in my dining room, I'll just leave this link to these initial results from my 55-300 and 16-85 zooms that I posted on the Pentax Forums:

https://www.pentaxforums.com/forums/122 ... ost4650922

The short version is that the Redrock unit is going to work for the purpose I bought it for, a quick macro adapter for outings where I haven't geared up for specifically macro shooting.

[Lou Jost]

Looks pretty good for its intended purpose!

[dickb]

I did a quick test of the RRM5X used as a closeup lens on my Sigma 150mm f/2.8 nonOS on minimal focus distance, with a Canon 5D mkii. In its normal orientation it is unusable at f/2.8, with massive amounts of spherical aberration (fogginess). At f/5.6 you get some improvement in the centre, stopping down further may help but I didn't test it. In reverse orientation at f/2.8 you get still some SA and CA. At f/5.6 you get a very good centre, with increasing SA and CA to the edges and corners. For comparison, the Raynox 5320pro was a little better when used in normal orientation, with the 3 dioptre lens closest to the Sigma, it has a slightly larger flat field but also some CA towards the corners.

[RobertOToole]

If there is any interest on the forum, there is a RRM 5x sitting here for someone, if it's okay by him, I might be able to find time to test it on the same target I've used in the past.

Since we are talking about tube lenses, I should mention that I have another TL sitting here that is a 240mm +4.2 that looks very good so far for only $14.99. The lens is made in Germany and so far it looks to be good to V. good IQ center to corner without any CAs issues. This FL with good IQ is very hard to find.

(Also I have just finished up a 135mm TL test with 5 or 6 objectives with some interesting results. Full report coming soon.)

Robert

[Lou Jost]

I've just tested the Redrock 5x as a full-frame tube lens with the Mitutoyo 7.5x. Very puzzling results. I'll start a separate thread for it, but the lens orientation that gave best results as a tube lens was the orientation which had terrible image quality when used as a stand-alone 180mm lens. On my copy, this was when mounted in reverse. Note that since the lens elements can be removed and reversed so easily, some of us may have versions in which the lenses had already been reversed.

When mounted in the forward direction, the lens is very sharp when used by itself. Whne used as a tube lens, that orientation gives a nice center but bad edges and corners with a lot of astigmatism. When mounted in the reverse direction, without the objective, the image at infinity is so bad that it is very hard to decide whether it is focused at infinity or not. I tried to get the best focus but I may not have gotten it right, the image was so bad. Yet in this orientation as a tube lens for the 7.5x, the results are great, and the corners are much better than in the "nice" orientation, though there is more purple fringing near the edges. This fringing can be almost completely removed automatically from the RAW files in ACR by checking "Remove chromatic aberrations". Now I will play with inter-lens distance and other variables to see if I can reduce the purple fringing further.

In forward orientation, bright white dust shows reddish fringing on the side toward the center of the image, and purple fringing on the side towards the edge. When the lens is reversed, these colors also flip, and the purple becomes more of an indigo.

Anyway, this is one of the best tube lenses I have tested for FF.

[rjlittlefield]

the lens orientation that gave best results as a tube lens was the orientation which had terrible image quality when used as a stand-alone 180mm lens.

I expect the stand-alone test was done wide open. Try stopping it down with an 11 mm aperture in the same position as the objective, and I'll bet that results then match what you get using it as a tube lens.

--Rik

[Lou Jost]

Yes, it was wide open. You're probably right. Will test when I am done using it with the objective. But even so, it was very sharp at infinity wide open in the opposite orientation.